It is 1974 and the chance encounter by Medhurst and Hagen with a stranger results in the man relating family mystery originating in a Catholic convent in Canada in 1919. Intrigued, Medhurst insists on following up the story via a former ATA (Air Transport Auxiliary) female ferry pilot now heading a major British aeronautical company.

When records show that four bodies were recovered following the fatal crash in Lincolnshire of a Lancaster bomber at the end of a ferry flight from Canada in 1943 the mystery deepens. All four bodies were burned beyond all recognition but only two personnel boarded the aircraft in Canada.

The pieces of the puzzle are slowly assembled and a tale of vengeance and murder slowly emerges. Culminating in Canada, the resolution of the mystery puts Medhurst, Hagen, and former ATA pilot Wendy in extreme danger.