A cruise ship loaded with passengers to the planet Azure collides with a trade ship as it comes out of warp, leaving the two ships merged but unstable. The Doctor, Romana and K-9 arrive to help out but discover there's also a problem with unidentified smugglers running a cargo of vraxoin, a forbidden organic drug that's as highly addictive as it is fatal. It instills the user with warm complacency and total apathy - the very qualities currently displayed by the cruise ship's bemused co-pilot.