The TARDIS takes the Doctor and Turlough to the London of 1702 where a mysterious highwayman roams the streets, a local occultist has made contact with the dead and gentlemen of fashion are disappearing, only to find themselves in a chamber whose walls weep blood... The time-travellers become enmeshed in the hideous plan of Sir Nikolas Valentine, a gambler at the mysterious Diabola Club who always seems to have a winning hand...