Writer Guy Adams like setting the Doctor a challenge or three, and his latest Big Finish main range title, The Quantum Possibility Engine, is no exception. Sylvester McCoy’s seventh Doctor has his work cut out when Melanie Bush (Bonnie Langford) steals the TARDIS and leave both him and Ace (Sophie Aldred) prisoners. Meanwhile Solar System President Josiah W Dogbolter (a toad-like capitalist alien played by Toby Longworth) is keeping things under control thanks to his Engine – surely nothing can go wrong with his perfect world?

If that weren’t all more than enough, enter Time Lord CIA agent Narvin (Sean Carlsen). Never knowingly helpful to the Doctor (at this stage) he completes a cast littered with fan favourites (Dogbolter himself is a character from several comics, and there is an extent to which he might be better appreciated if you’re not coming to him for the first time. It’s not a big obstacle, and director Jamie Anderson makes sure the cast are on sparkling form with the energy of the story letting the action fizz along as time / history / memory are all subject to flux as the mighty Engine does its thing.

To add even more colour to the story, Dogbolter has his own, more local problems as the Krasi are invading / conquering / liberating the oppressed citizens and have their eyes on the Engine as well.

It’s all a bit mad, lots of fun, and has some great performances with Jules de Jongh adding edge as the Captain Regent of the Krasi, but a story this big has a natural conclusion, not so say it isn’t very enjoyable and challenges the characters (and actors) on the way. Once matters are resolved, will this TARDIS crew ever be the same again? This story is the third in a set of five seventh Doctor adventures in a row, though the last with this crew for the moment, so we shall have to wait and find out how they move forward, if they can.