The party descends the spiral stairs into a round room of the same metallic construction. The floor rings solidly, unlike the upper decks, and a section of the wall has been crushed in by solid rock as though the entire structure rests on this overburdened lowest level. Sliding doors ring the chamber. The damage from intruding rock exposes a surrounding cavern.
Glowing fungi in the cavern attract Shroom’s attention. When he attempts to collect some into a jar, Shroom realizes the cavern wall he is scraping is actually a camouflaged cave ape covered in the glowing fungi. The scraped ape bites deeply into Shroom. Three more hiding cave apes pounce on Bizzle and Shroom. Now it’s on, like some kind of mashup of a pack animal and a giant simian rolling barrels down a deranged structure in an attempt the prevent the party from advancing.
Tricksy, already standing on the wall ready with her shortbow for whatever trouble Shroom stirs up, marks and shoots the closest ape. Tatters joins in with a firebolt. Shroom hammers away with symbiotic entity and a halo of spores trying to barely kill the apes just right to raise them as zombies, but Bizzle finishes off the first ape before Shroom can capture it. Slick runs in swinging his great axe. An ape runs to meet him, but the axe gets loose and sails overhead embedding into the already dead ape.
While the party is distracted by the cave apes, a mind flayer creeps up behind Tatters and attaches to his face. Tricksy scrambles across the wall to get away, putting arrows into her new mark. Tatters blasts a thunderwave, but the flayer maintains his tentacle grip. Tatters avoids the tentacles probing for his nose while Tricksy plugs the flayer with arrows. Tatters gives the flayer a second thunderwave and finally knocks it back, dead.
Bizzle moves to help disarmed Slick and drops the attacking ape, but this leaves two apes beating down Shroom. Shroom crams a salvage bar into his mouth and puffs a halo of spores over one of his assailants, zombifying it. Slick retrieves his magical great axe and plants it into the last fighting ape. Tatters splashes the ape with acid and Bizzle cuts it down. The apes have rough jewels embedded into their foreheads.
The party explores a passage the mind flayer exploited to ambush Tatters. Bizzle checks through the fallen mind flayer’s possessions and comes up with a magical sword. Vaguely aware of the tendency for his scimitars to liberate other weapons, Bizzle proposes someone else carry the magical sword. Tatters accommodates, strapping the longsword to his small gnome frame.
Shroom sends his zombie cave ape pet, Fubca, to beat down one of the doors. Tatters reaches out to Apholatzin with the helm of telepathy to inquire about artifacts and the possibility of opening some of these doors. Apholatzin offers Tatters all the rings he could carry as an incentive to depart. Fubca breaks through the door exposing piles of treasure, including rings. Tricksy points to a pair of cave apes lurking at the back wall. Tatters tosses a fireball at them. Shroom’s ice knife, Tricksy’s arrows, and Tatters’s ray of frost drop one ape, Slick’s sneaked great axe and Bizzle’s scimitars drop the other.
Shroom collects fungus while Bizzle uses a pan from his mess kit to scoop piles of rings into his greycoat. Tricksy hears the sound of a door opening and closing signaling the escape of a person of interest. She pries at the door with a dagger while Tatters freezes it brittle. Shroom gallops up riding Fubca who smashes down the door. Bizzle gives chase and finds the fleeing mind flayer in the next room. Shroom gallops by on Fubca with a hearty, Never bathe! Fubca and Shroom claw at the mind flayer with primal savagery.
The mind flayer blasts a psionic attack that stuns Bizzle and Tricksy and kills Fubca. Atop crumpling Fubca, Shroom lands on his feet in time to take a parting warhammer hit as the mind flayer flees the room. Shroom and Tatters pursue. Shroom captures the flayer with a halo of spores, releasing Tricksy and Bizzle from stunnation.
Shroom and Tatters can see a sunken room pooling a brine solution and occupied by a giant elder brain. Giant elder brain Apholatzin is accompanied by yet another mind flayer. Shroom sends his new mind flayer zombie pet in to feed on the giant elder brain. Apholatzin lashes out with a psionic attack stunning Tatters and killing the zombie. Slick puts a crossbow bolt into Apholatzin. Tricksy scales a wall. Shroom pokes his head in to cast confusion, but Apholatzin maintains well-ordered thoughts. Shroom ducks back out. The mind flayer finds him and attaches itself to stunned Shroom’sface. Bizzle blinks into shadow and slips up to Apholatzin.
Bizzle blinks back into material existence and beats on Apholatzin in scimitar double time. Apholatzin seizes scimitar Destra with a tentacle. Slick and Tricksy attack the mind flayer in an attempt to spare Shroom, but the flayer pulls his brain out of his nose collapsing his skull. Apholatzin grapples Slick with a slapping tentacle. Tatters gulps down a salvage bar. Tricksy finishes the mind flayer, but not in time to save the late Shroom.
Apholatzin becomes the sole recipient of attacks from Bizzle’s free scimitar, Tricksy’s marked arrows, Tatters’s witchbolt, and Slick’s greataxe. Apholatzin pops out into another, presumably safer, plane, very nearly taking the gooder half of Bizzle’s prized scimitar collection. Bizzle blinks into shadow hoping to confront Apholatzin there, but Apholatzin has escaped.
The party explores around and discovers an eclectic trove of artifacts: a small wooden chest containing a desicated eyeball, a monstrance, a chakram, a staff, and a small jar. Tatters collects the artifacts into his greycoat, confident that the chakram is the “ring” sought by their patron, Baron Van Fostern.
Bizzle retrieves Shroom’s Plan B [option 4] and smacks it approximately in the former location of Shroom’s deflated forehead. Shroom is completely restored, growing a brand new brain. Shroom removes any doubt as to his authenticity when he collects his old brain from the tentacled gob of the dead mind flayer. Classic Shroom.
From what the party can piece together, the structure is a crashed nautilus, a ship of mind flayers. Apholatzin the elder brain grew from a cultivated illithid, fed by the constant supply of Chult treasure hunters.
The party returns to R&S victorious and wealthy, but unknowingly incubating a brain fluke in Tatters’s prodigious brain.