Can the Doctor, now in his fourth incarnation, recover from his post regenerative trauma to save the Earth from Think Tank and their plot for world domination ?

The Doctor and Sarah Jane become convinced Think Tank are behind the electronic component thefts but are unable to stop them carrying out another raid.

Sarah Jane and Kettlewell infiltrate an SRS meeting to try and find out what Miss Winters is up to but there is a surprise in store.

UNIT attempt to get into the bunker to stop Miss Winters setting off the world's nuclear missiles but first they have to get past the K1.