Welcome to Wetworld: a tropical paradise with scenic lagoons, amphibious locals, and a mild case of murderous slime infestation.
Short Synopsis
The Doctor and Martha land on the waterlogged colony planet of Sunday — a vacation spot gone terribly, spectacularly wrong. The local amphibian residents are being puppeteered by alien parasites, the terraforming process has flooded the settlements, and the Doctor’s hair has officially given up the fight against humidity.
Extended Storyline
The TARDIS touches down (well, splashes down) on Sunday, a once-promising human colony planet now resembling a planetary-sized puddle. Terraforming machinery gone haywire has turned most of the surface into swampy chaos. Martha’s first words: “This isn’t exactly a beach holiday.” The Doctor cheerfully replies, “Nonsense! It’s brilliantly soggy!”
Their first encounter is with the Paladion, a species of humanoid amphibians trying to coexist with human colonists. Relations have been — to use a diplomatic term — damp. The humans blame the Paladion for sabotaging their machines, while the Paladion think the humans are reckless fools turning their world into soup.
It all gets worse when something slimy starts crawling out of the water. Literally.
An ancient alien species known as the Gappa (not to be confused with the Japanese kaiju — though the Doctor does make that joke) has been awakened beneath the planet’s surface. They’re microscopic symbiotes that hijack host bodies, converting them into part of a growing biomass. The Paladion were trying to contain them… until human meddling let them loose.
The infected begin to mutate, forming grotesque hybrid creatures — half-human, half-amphibian, all nightmare. Entire settlements vanish beneath the wetlands. The Gappa communicate through eerie whispers in the water, promising “unity” and “peace” in the most unsettling way possible.
Cue the Doctor and Martha diving headfirst (and somewhat reluctantly) into the mess. The Doctor’s sonic screwdriver takes a swim, Martha’s shoes are ruined, and the TARDIS is half-submerged, which the Doctor calls “a design flaw in my piloting, not in the ship.”
Martha befriends Krinth, a Paladion scientist trying to save his people, and together they uncover that the Gappa have merged with the planet’s bio-engineering systems. They’re not just infecting people — they’re rewriting the terraforming network itself, turning the whole planet into one giant, living organism under their control.
The Doctor realizes the only way to stop it is to overload the central terraforming core. Problem: it’s at the bottom of a flooded reactor pit swarming with Gappa-infected hosts. Solution: he dives in anyway, muttering something about “taking a quick dip in sentient soup.”
In a gloriously chaotic finale, the Doctor manually triggers the system’s feedback loop, frying the Gappa network with a massive pulse of radiation (and quite possibly sheer defiance). The colony’s waters boil into mist, the parasites dissolve, and for once, everyone manages to survive.
As the steam clears, the Doctor and Martha stand knee-deep in muck, looking out over the newly calm waters. Martha asks if the Gappa are truly gone. The Doctor pauses, grins, and says, “Let’s just say if they resurface, I’ll bring snorkels next time.”