Third big-screen adaptation of John Buchan's classic novel. Mining engineer Richard Hannay (Robert Powell) is on a brief visit to England when his neighbour Colonel Scudder (John Mills) warns him that foreign 'sleeper' agents are at work, planning to pre-empt global war by murdering a foreign dignitary. When Scudder is murdered by the agents Hannay finds himself under suspicion by the police, and goes on the run in a bid to both prove his own innocence and expose the enemy spies.

Sylvester McCoy makes his first appearance as the venerable Doctor, coming up against his old enemy, renegade Time Lord Rani (Kate O'Mara). She forces the Tardis to crash land on Lakertya, and then masquerades as his assistant Melanie (Bonnie Langford), tricking the newly regenerated Doctor into constructing a giant time manipulator designed to drain the minds of history's greatest scientists.

An early adventure for everyone's favourite time traveller. When the TARDIS lands on the planet Marinus, the Doctor (William Hartnell), Ian, Barbara and Susan are captured by Arbitan, Keeper of the Conscience of Marinus. The Conscience is an all-powerful machine which controls the planet in an attempt to regulate crime, but it requires four missing crystals to complete its function. Otherwise, the machine could fall into the hands of the Voord, led by the evil Yartek. The TARDIS crew are thus charged by Arbitan with recovering the crystals before it is too late.