Fresh from solving a spate of murder mysteries, Diana Bakewell and Zaf Williams are separated when Zaf goes on a course to gain his qualification as a tour guide. The course is at London's iconic St Paul's Cathedral, which Zaf is expected to get to know so he can be tested on his tour guide abilities. Meanwhile, Diana is forced from her wonderful London home by her unscrupulous landlord.

But all this has to be put aside when a resident at a local hostel is found dead, apparently poisoned. More perplexing is the fact that, after a police investigation, Diana realises she saw the victim walking around hours after he had supposedly died. 

Zaf and Diana have a mystery to solve at St Paul's, one in which the victim was a known thief of religious treasures.

Can they get to the bottom of the crime before the killer strikes again? Will Zaf need to enlist the help of his fellow tour guide trainees? And will they uncover the reason why the victim was there in the first place? 

Find out in Diana and Zaf's fifth mystery, full of mysterious twists, iconic London landmarks, and naughty cats.