May 1971, and a cab driver is found dead in his taxi, owing a large debt to a colleague.
Investigations into his death leads Endeavour and the team first to a nudist colony, where guests are making the most of the spring sunshine, and later to the heart of a blue movie outfit in London's Soho.
Meanwhile at home, Endeavour receives a guest who reminds him of a past he'd sooner forget. As the investigation into the cab driver's murder unfolds, Endeavour starts to retreat from those close to him and appears set on a course of willful self-destruction.