The Armchair Detective and the Castle of Mandrake Part One: Series Two

First ever Armchair Detective two-parter:

"Events cast shadows before them."

Old Tom, most unlike himself, is suddenly fearful of the 'Old Days'. He eagerly looks into Trench's new mystery to take his mind off his worries.
The investigation takes Trench and Debsy away from traffic duty to a detective agency who are monitoring the strange case of a wife who disappears every Tuesday night.
And just who is watching Trench from afar?

Old Tom slowly realises that he must solve the mystery before his past catches up with him...