The Doctor, Romana, and K9 arrive on a space liner that has just collided with another ship due to an accident upon leaving hyperspace. The navigator of the space liner was off his face on a drug called vraxoin, hence the collision. Somebody's smuggling the drug on board too. As if that wasn't worse enough, a scientist on board had a machine that he invented that keeps samples of alien ecosystems in pocket universes for observation. A group of dangerous creatures called Mandrels escaped from the machine and started killing the crew and passengers.
This story is one of those that has a reputation of not being very good. I'm probably one of the minority that think this story isn't all that bad. Sure, the acting is a bit spotty in parts, and the Mandrel costumes are noticeably tatty, but that's all part of the fun sometimes. Then again, I liked The Twin Dilemma (readers of Doctor Who magazine voted it the worst ever Doctor Who story). Does that make me a bad person?
Highlights include Tryst the scientist's comedy accent, whatever it may be. Is it German... Dutch? Whatever, it was pretty fun. I have to mention Tom Baker's performance as the Doctor. A bit silly in part, but when the ones responsible for smuggling the vraxoin are carted away from the authorities, his underplaying of the situation is chilling. There's nothing scarier than a quiet Forth Doctor.
Also, well done for Bob Baker for making the story's message (drugs are bad) not as blatant as some of the other stories that have had very special messages. *cough-The-Happiness-Patrol-cough* We weren't beaten about the head by the message. Some of the messages in other Doctor Who stories have been as subtle as a Mandrel in the face.
Lowlights include Romana's outfit. What the hell is that grey... thing? I much preferred the pink version of the Doctor's outfit that she wore in Destiny of the Daleks.
All in all, an adequate story. Not one of the Forth Doctor's best, nor is it one of the worst. Watch it if you want a Doctor Who story with a message that doesn't beat you around the head or laugh at some of the sillier moments.