The TARDIS arrives on the interstellar cruise ship Empress, which has emerged from hyperspace at the same co-ordinates as the trade ship Hecate, causing a dimensional crossover. The Doctor offers to help separate the two craft. Captain Rigg (David Daker) of the Empress doesn’t really believe the Doctor is a Galactic Salvage rep but agrees to let him reverse the smaller ship at full thrust. The co-pilot Secker (Stephen Jenn)—a Vraxoin addict--is attacked by a clawed monster and left for dead. K9 is used to cut through the locked ships.
On board the Empress are a zoologist named Tryst (Lewis Fiander with a strange accent) and his assistant Della (Jennifer Lonsdale) who use a Continual Event Transponder to store portions of planets on electro-magnetic crystals, which allows one, not only to monitor, but to enter the landscapes. Their most recent stop was on the planet Eden, where a member of the expedition was killed. Romana looks at the Eden projection and see eyes staring out of the jungle, then an insect stings her.
The Doctor and Captain Rigg find Secker and send him to sickbay, but too late to save his life. The Doctor finds his drug stash, but someone stuns him and steals the evidence. When he comes to, he returns with Rigg and K9 to cut through the power source, but a roaring creature comes through the opening. K9 repels it while the Doctor and Rigg work. Rigg is sure there are no drugs on his ship, but when Romana wakes up, someone spikes her refresher drink. However, Rigg drinks it instead of her and shows signs of addiction. The Doctor pursues a silver-suited stranger through the two ships, but loses him, through he finds his radiation badge, which proves he was on Tryst’s expedition. Tryst accuses Della of smuggling the drug, with her late partner Stott, who died on Eden. Azurian planetary Customs and Excise officers (who seem at times to be doing a Monty Python skit) board the ship, and naturally suspect the Doctor of smuggling because there are traces of Vraxoin on his clothing. The Doctor and Romana flee into the Eden projection, where they are menaced by sentient jungle plants and clawed monsters called Mandrels. They meet up with Stott (Barry Andrews) who is not dead after all and takes them to his cubicle. He is a Major of the Space Corps and has been hiding in the projection while trying to track down the source of the drugs. They all return to the Empress, pursued by the Mandrels, who are killing passengers.
The Doctor, Romana, and K9 evade the creatures and try to separate the spacecraft while avoiding getting arrested. When the Doctor incinerates one of the Mandrels, it turns into raw Vraxoin, answering that question. Finally, the Doctor separates the craft, but he disappears. The pilot of the Hecate, named Dyhold (Geoffrey Bateman) is complicit in the drug-running, and the Doctor finds evidence on the Hecate. They both return to the Empress. Romana tells Della that Stott is still alive, but Della is arrested.
The Doctor believes Symond is working with Tryst. When the narcs try to arrest the Doctor, Stott warns them to back off. Tryst is reunited with Della and confesses his part in the smuggling racket. The Doctor rounds up the Mandrels with K9’s dog whistle and leads them back into the Eden projection. He traps the smugglers and leads them to the Customs agents. The ships separated and the mystery solved, the Doctor and friends restore everything to their home planets, hoping that the Mandrel’s drug secret remains hidden.
The Mandrels were not well received to put it mildly. The Doctor Who Appreciation Society called them “cute rejects from the Muppet Show.” And some of the sets seemed rather cramped and shabby for an interstellar cruise ship (this is fairly common in Doctor Who, I’m afraid, where the bridge of a futuristic spaceship often looks more like a collection of lawn furniture). The jungle sets, on the other hand were highly praised. The discussion of the serious matter of drug-addiction was appreciated. There were troubles on set that ended with the director being fired; the cast and crew came back from tea-break and he was gone. The Continual Event Transponder contained portions of the planets Eden, Gidi, Zil, Bros, Vij, Darp. Lvan, and Ranx. Some of the landscapes in the machine are of Terra Nova in Space 1999.