A community service group find themselves under suspicion when one of their members, car salesman Eddie Morris, is pushed off the tower of a ruined castle around which the group are working. John and Janie are brought together by DCI Clarke to solve the case. However, following the shocking revelation that John has been dating Janie's mam, Yvonne, tensions remain high between the two. Though they haven't spoken in months, our crime-fighting duo must now remain professional if they hope to solve Eddie's murder.

Janie tries to give the case her full attention while getting to grips with the demands of her new, long-awaited promotion to detective inspector. As if this weren't enough, she's also living with pathologist Baxter, having moved out of her mum's house as an act of rebellion while Yvonne continues her relationship with John. Meanwhile, John employs a different tactic for the investigation by going undercover, as himself, in the community service group. John hopes to gain a better understanding of the suspects and use his signature character analysis to seek out the guilty party.

In the community service group, John and Janie question their list of suspects, which include the deceased's spiteful ex-wife, a sarky young offender, a hardened criminal, a disgraced Welsh politician and their happy-go-lucky supervisor. With mounting pressures, both personal and professional, will Janie and John be able to put their differences aside and solve the mystery?

On the set of an epic Welsh TV drama, The Mabinogion, a runner is found dead in a young starlet's trailer. John and Janie are called to investigate the crew, and as they journey into the glamorous world of TV production, Janie finds herself starstruck by the actors, while John is simply struck by how much of an outsider he feels.

They begin their interviews with the young lead of the show, Welsh actress Olivia Whitmore, who, to Janie's surprise, is incredibly down to earth. She and Olivia click immediately, causing John to question whether Janie is able to put her personal connection aside and stay open to all suspects. Janie's potential conflict of interest is soon put into perspective, however, when they encounter the next interviewee, Randall St Clair, the actor who played John's old Caesar sidekick, who is a little frostier with John than expected. The duo explore the rest of the crew, which includes a stalactite-obsessed set designer, a laddish medic and an old-school make-up designer.

On-set injuries, secret affairs and badly behaved owls all lead Janie and John towards the answer. But forced back into the world of his former life, can John summon what's needed to uncover the truth, and can Janie remain professional when her new friend is a prime suspect?