The culvert swallows him whole.

  Jim squeezes through the rust-gnawed gap in the grate, claws scraping for slick purchase on stone. The alley light dies behind him in three frantic heartbeats. Then the world collapses to gray-on-black, lit only by the faint spill from above and the low-light glow his new eyes pull from nothing.

  The sound hits next.

  Water. Always water—trickling, dripping, rushing somewhere deeper. Echoes layer and twist until it’s impossible to tell what’s close and what’s far. Every tiny splash sounds like something big taking a careful step.

  He forces himself forward anyway.

  The culvert slopes down and opens into a first chamber. Not huge, but big enough that the acoustics change. The ceiling lifts out of reach. The smell punches up another level—sour, thick, layered sewer stink: old waste, rotted food, fish guts, human filth, alchemical discharge, all cooked together into something that could strip paint off a shield.

  Jim’s whiskers twitch so hard they almost hurt. The rat body wants to spin and bolt. The human brain just notes, calm and dry: Yep. This tracks.

  The chamber is roughly circular. A central channel of dark water gurgles through a shallow stone trough. A narrow ledge runs around the edge—maintenance walkway for humans, death-trap runway for one deeply unfortunate rat.

  He tests the ledge with one paw.

  Slime.

  Not instant-death slime, but enough to make every step feel like a bad roll waiting to happen. Somewhere in the back of his skull an old DM voice mutters: DC 10? 12? Whatever—just don’t roll a one.

  He hugs the wall and moves slow.

  On the far side, two tunnels branch off: left and right. Behind him the culvert he came from makes three exits total.

  He pauses at the junction and lets his nose take over.

  Left tunnel: cool, steady water smell. Rat scent too—but thin and recent, like only a few have passed lately.

  Right tunnel: stronger rat smell, heavy with panic-sweat under the musk. And under that, something sharper—chemical tang, eye-watering. Alchemist’s dump? Weird fungus? Too early to tell.

  He’s still weighing when his ears flick to a new sound—plip… plip—something small hitting water nearby.

  He freezes.

  Tiny shapes float past in the channel below the ledge. At first he thinks leaves or trash. Then one bumps the stone and rolls just enough.

  Fish. Or what used to be fish.

  Half-eaten, ragged, drifting like torn little flags. He counts without meaning to.

  One. Two. Three… seven.

  Seven sad, half-eaten sewer-fish bodies bobbing past like an omen.

  He stretches his nose toward the water without getting close. Not rat bites. The edges are too ragged, too… melted. Flesh slumped like wax held to a flame.

  His fur prickles.

  Great. Either something with terrible teeth or something that dissolves dinner. Classic sewer options.

  A faint glistening smear clings to the underside of the stone overhang by the waterline—translucent slime, almost invisible unless you’re looking straight at it.

  Slime. Oozes. Puddings. He’d thrown them at players for years from behind a screen. Meeting one at eye level feels different.

  He stays very, very still and listens.

  No new splashes. No creeping squelch. Whatever left the mess isn’t here right now. Just passing through. Or sleeping deeper.

  Above the waterline, carved into the stone: a rough circle with spiked rays, gouged deep, then half-chipped away. Still recognizable if you know what to look for.

  Eye. Spiky rays.

  Xanathar. One of the beholder’s sewer routes passes through here.

  Underneath it, newer and cruder, scratched with something smaller: a cluster of tiny lines like stick-legs around a blob body. If you squint—and he is, specifically, a rat—it looks kind of like… a rat.

  Somebody down here is leaving signs.

  He files it.

  Right now, first-room rules: don’t die, don’t slip, don’t alert anything you can’t outrun. He edges along the ledge, keeping all three exits in view—left tunnel, right tunnel, the way back to daylight.

  He glances over his shoulder one last time at the distant, memory-small slice of sky.

  Then Rat #1 turns his back fully on the Drowned Roach and pads toward the deeper dark of the right-hand tunnel—following the stronger rat scent, the faint sting of strange chemicals, and the first real thread of story the sewers of Waterdeep have offered him.

  The right-hand tunnel narrows fast.

  Jim pads along the slimy ledge, back brushing rough stone, whiskers tasting every shift in the air. Behind him the first chamber fades into echo and stink. Ahead the chemical tang sharpens, layered over with rat musk and something singed.

  The ceiling drops until it brushes the fur along his spine. The central gutter grows shallower, choked with debris: straw, splinters, fruit rinds, and unidentifiable blobs his human brain refuses to name.

  Sewer décor.

  The rat scent grows heavier, but it isn’t the calm background of a happy nest. This is stress-scent. Fear. A lot of little bodies panicking in a confined space.

  He slows.

  Light ahead—just a suggestion, a ghostly green glow around the bend. Not torchlight. Wrong color. More like someone bottled radioactive algae and spilled it.

  His gamer sense starts ringing a quiet hazard bell.

  He edges to the corner and does the classic adventurer move: only nose and one eye around it.

  The chamber is smaller, busier.

  The central channel widens into a shallow basin, water barely ankle-deep for a human, chest-deep for a rat. In the middle floats the source of the glow: a sluggish swirl of phosphorescent slime clinging to the surface and the stones like a slow-motion oil spill.

  The genuine version of this novel can be found on another site. Support the author by reading it there.

  Trash drifts trapped inside—twigs, fish bones, something that used to be a leather glove.

  The air stings his nose. Not lung-burning, but enough to make his eyes water. Some alchemist topside has been dumping failed experiments here for a while.

  On the near ledge, clumped together, are rats.

  Half a dozen at a glance, maybe more: damp fur, hunched bodies, eyes too wide. They’re all pressed back from the water, staring at the glowing patch like it might leap out and eat them.

  One limps badly, hind leg half-dissolved to a shiny stump. Another has patches of fur burned away, raw skin showing. They smell like pain, fear… and recognition.

  One sees him.

  A brown head swivels. Black eyes lock on. Whiskers twitch. A short, sharp squeak—Who?

  Normally Jim would read it as generic “stranger, same species.”

  But something in his skull shifts.

  The character sheet flickers at the edge of his vision, not fully open but enough to remind him: INT 13. Human mind. Languages understood: Common, Elven, Dwarven, Goblinoid. No “Rat” listed. He doesn’t need it. Instinct plus human pattern-matching does the rest.

  He answers with careful squeaks, posture low, ears half-back.

  Not threat. New. Came from up.

  The rat stares. Then, slowly, relaxes enough to stop looking like an unstrung bow.

  Jim creeps closer along the wall. The glow paints everything sickly green, turning fur into ghost-shadows. Up close the damage is worse: at least three rats have chemical burns. All of them wear the wild-eyed look of creatures that just learned “environmental hazard” is a real category.

  His human side translates their body-language babble.

  Burned Rat: Bad water. Bad. It moved. It ate Siv.

  Limping Rat: Siv tried to cross. Siv is gone. Water is wrong now. Tunnel is wrong.

  A younger one squeaks from the back, tail twitching spastically. We used this way. Nest deeper. Water changed. No way past.

  Jim looks at the basin.

  On a normal day this would be a simple rat path: hop down, splash through, scurry up the other side. Today it’s fluorescent sludge roulette. The stuff isn’t aggressively mobile—but it clings. Step wrong and you carry it with you. Onto fur. Onto skin. Onto everything.

  He remembers the half-eaten fish from the first room. Same bite pattern. Same melted edges. Whatever’s in that sludge is not here to high-five his immune system.

  The ledge curves around the basin in a narrow, treacherous arc. Barely enough room for a rat to edge along without paws slipping into the glow.

  Barely.

  His rat body edges back on pure instinct, tail curling away from the light. Every nerve screams nope in stereo.

  His human brain is already calculating ledge width, slime spread, splash radius, rat-paw friction.

  Also, slightly annoyingly, loot potential. Adventurers pay good money for weird glowing alchemical samples, right?

  He shakes the thought away before he does something suicidally on-brand.

  One of the less-burned rats creeps closer, sniffing high-speed. Hope flickers in the posture, faint and twitchy.

  You from other tunnels? Safe tunnels? Is there out?

  Jim feels the question like a small weight. Up in the Drowned Roach he gave one tired human a tiny miracle in the form of a “found” wine crate. Down here it’s the same energy, just with more whiskers.

  He glances back the way he came—toward the first room, daylight far behind. Forward is nest, danger, whatever changed the water. Back is “find another route” and “maybe never see these rats again.”

  Isekai cheat brain and rat instincts have a quick, loud argument. Then GM brain cuts in with the deciding factor:

  If something is changing the sewers, I need to know what it is. Sooner. From a distance. Before it gets worse.

  He studies the ledge again.

  Slippery. But walkable. If he hugs the wall, takes it slow, and doesn’t flub it, he can get around without touching the sludge.

  If.

  His human self, who has rolled too many natural ones at too many tables, winces quietly.

  He looks at the burned rats, at the glow, at the tunnel beyond—dark but thick with their scent. Their nest. Their world. Cut off by someone pouring magical bad ideas into their only path.

  “Okay,” he thinks. “Fine. We’re doing this the stupid way.”

  He plants his paws at the start of the ledge, feeling the slime-slick stone under his pads. The wall is rough enough for a bit of extra grip. He can almost hear dice clattering in the background of his brain.

  Balance check. Reflex in the back pocket. Classic.

  He draws in a breath that smells like chemicals and fear, and takes his first careful step along the narrow rim above the glowing water.

  Jim teetered on the edge of the ledge, staring down at the glowing sludge, and then his brain did the thing it always did:

  Wait. I have a cheat.

  He eased back from the risky path, ignoring the questioning squeaks from the other rats, and crouched at the very lip of the basin where the slime clung thickest to the stone.

  Up close it was nastier: viscous, like half-set jelly, faintly pulsing with its own rhythm, smelling like someone had melted a wizard’s lab and poured it into a gutter.

  His instincts screamed do not touch, which was exactly when the gamer part of his soul went, so what if you just barely touch it?

  He stretched out one forepaw. Just the tip of one claw.

  The instant the claw broke the surface, agony flared up his leg — sharp, stinging, like dipping his hand in industrial cleaner. His whole body jerked back on instinct.

  At the same time his vision exploded with UI.

  A shimmering outline whipped across his field of view, racing over the entire glowing mass: every tendril on the stones, every slick on the water, every droplet clinging under the lip of the basin. The system grabbed it all as one object.

  [Interactable object detected.]

  Alchemical Sewer Slime (Unstable) – Hazard

  Status: Non-living, cohesive mass. Eligible for storage.

  His inventory square pulsed, empty and waiting.

  Jim’s eyes watered, both from the fumes and from the very immediate pain in his claw.

  “Okay ow ow ow—STORE NOW.”

  He didn’t have to say it. He just clamped down with the same mental motion he used on the cork and the crate.

  Blink.

  The world hiccupped.

  The glow vanished.

  Every smear of phosphorescent sludge just wasn’t there anymore. One moment there was a sickly green sheen across the basin; the next there was only bare, scorched stone etched and pitted where the slime had sat, normal disgusting sewer water dark and opaque but not actively sizzling, and a few sad half-melted fish carcasses slapping wetly onto exposed rock as they dropped out of suspension.

  The room plunged into near-black. For a heartbeat everyone—Jim, the injured rats—froze.

  Then his inventory square reappeared in his mind’s eye, now cheerfully full:

  [Inventory 1/1]

  Alchemical Sewer Slime (Unstable Hazard)

  – Volume: “Too much”

  – Properties: Corrosive, phosphorescent, mildly toxic vapors

  – Handling: Strongly discouraged

  His claw throbbed. He lifted the paw and inspected it: the very tip of the keratin was eaten away, the claw shortened and raw, but the flesh above was mostly okay. Painful, but not crippling.

  Call it 1 HP worth of “don’t do that often.”

  Behind him the rats lost their tiny minds.

  There was a burst of squeaks and chittering, high and frantic. From their perspective: tunnel blocked by glowing death-water, stranger rat arrives from “above,” touches bad water, bad water disappears.

  The burned one who first spoke to him stared, eyes reflecting the faint residual glimmer on the wet stone.

  His body language shifted slowly from fear to something else. Not quite dominance, not quite submission.

  What are you? the posture asked, awe-tinged.

  Jim answered with his best approximation of “totally normal rat, don’t mind me” while also trying not to look like he was hiding a portable apocalypse in his soul.

  He settled on low posture (not claiming boss), tail relaxed, ears forward. A friendly stranger who just happened to have broken physics.

  He gestured with his nose toward the now normal-ish basin.

  Without the slime the crossing was back to being a regular sewer problem. The water was foul, but not lethal. It slapped gently against the stone edges, a few inches deep at worst. For a human, ankle-soaking. For a rat, chest-high in places—unpleasant, but doable.

  The limping rat moved first.

  He crept to the edge, sniffed, ears flat. No sting in the air now, just the usual sewer cocktail. He padded down into the water, squeaked once at the cold, then waded across in a stuttering little trot.

  Nothing melted.

  The others followed, emboldened, splashing through. Their burned patches didn’t flare up; the raw skin was unhappy, but not getting worse.

  They clambered up the far ledge, shaken but alive, and gathered there, looking back at him.

  The battered one squeaked a short phrase that his brain rendered as something like Come. Den this way. Safe… if still safe.

  Jim glanced back once at the tunnel he came from, toward faint air currents that hinted at the world above.

  Then he looked down at his inventory square—at the words Alchemical Sewer Slime (Unstable Hazard)—and at the scorched stone where it used to be.

  He had, in his pocket dimension, a sewer-wiping weapon that could erase doors, enemies, and probably relationships if deployed carelessly.

  He also had exactly five hit points and a shortened claw.

  “Right,” he thought. “New life goal: never trip while holding that.”

  He stepped into the foul water.

  Cold filth seeped into his fur, clung to his belly. The current pushed just enough to be annoying. His feet slipped on slime-slick rock; he had to splay his toes wide to keep balance.

  It was disgusting.

  It was also a victory.

  He hauled himself up onto the far ledge, dripping, and shook vigorously, spraying the nearest rat with a fine mist of sewer. They endured it with the stoicism of creatures who had lost more than dignity recently.

  As a group they turned and started down the tunnel deeper in, toward their cut-off nest, toward whatever had been changing their world.

  Rat #1 padded along with them, one more shadow among many, eyes bright in the dark, pockets full of stolen catastrophe.

  The sewer behind him gurgled on, unaware that a significant portion of its threat budget now lived inside a single, slightly crispy rat.