Convict In Space is the 16th produced episode and the 16th Broadcast episode of the series Fireball XL5
Grothan Deblis, the spy, steals some top secret plans, but is captured by the crew of XL5 and sentenced to twenty years imprisonment on the prison planet Conva. Mr and Mrs Space Spy trick Steve Zodiac and capture Professor Matic to force Steve to hand over Dedlis, whom they plan to trick into revealing the whereabouts of the plans.
Deblis takes them to the volcanic planet Voldanda where he has hidden the plans. He double-cross Mr and Mrs Spy and Steve is able to rescue Professor Matic and recapture Deblis.
- The XL5 crew are able to recognise the S.S. Thor and are aware that it belongs to Griselda and Boris, so this episode must be seen after Spy In Space, where they do not know of the Thor's ownership.