Rather good story where the Doctor and his companions land on the world Marinus, where a supercomputer once ran everything, but went wrong and was shut down.  A  scientist has fixed it, but needs the assistance of the visitors to secure 5 keys to start the machine.  What follows is a set of contained separate stories as the visitors traverse the world to collect the disks.  These range from very good to good, each story holds up quite well – though there’s some weak scenes and the final two episodes are a little overextended, centring on a murder mystery.  My favourite is the first substory – where brains in glass jars have mental control over the humanoids in their city, making the visitors think they are in paradise when they are in fact in rundown shabby rooms, until Barbara suddenly sees through it.

I rather liked it overall.

Rating: Good, 6/10