A new adventure awaits as DI Humphrey Goodman and Martha leave London for Devon. Humphrey dives into his first case, which involves an unusual prime suspect: a 17th-century witch.

Humphrey and Martha throw themselves into work in an attempt to distract themselves from recent events. For Humphrey, this means investigating one of the strangest cases he's ever encountered: an entire family have vanished from their house, with the TV and lights left on and dinner half-eaten. Meanwhile, Martha nervously prepares for the opening of her new café. Racing against the clock to get it all ready, she is dealt a blow when the bank call to refuse her loan, and her situation isn't helped by Humphrey's impulsive decision to blow their savings on a ramshackle houseboat. Help comes from an unlikely place: local vineyard owner Archie Hughes, who also happens to be Martha's ridiculously handsome ex-fiancé, volunteers to become a partner in the business. This could be the answer to Martha's prayers, but how will Humphrey react?

The community of Shipton Abbott is rocked when a beloved painting disappears in a seemingly impossible heist. Humphrey tries his best to find some common ground with Archie.

Humphrey and the team face one of their strangest cases yet when a dead man is found in the centre of a crop circle. No-one knows who he is or how he got there. Conspiracy theorists suggest aliens are to blame, which seems possible when footage emerges of mysterious lights hovering above the field, but pragmatist Esther is sure that the answer lies closer to home. Brother and sister Andrew and Cassie Parker own North Farm, where the body was found. Do they know more than they're letting on? When the investigation leads the team to the site of an illegal rave, they're reunited with a familiar face who just might be the key to cracking the case wide open. Meanwhile, Martha faces her own professional challenge as her café is visited by a food critic. With Archie's help, she rises to the occasion, but in doing so, misses an important IVF appointment with Humphrey. Given pause for thought, she starts to question what she really wants. Archie, however, misreads Martha's uncertainty for something else, which has unforeseen consequences.

Panic spreads throughout Shipton Abbott when an arsonist targets three local businesses, scrawling 'PIG' at the scene of each fire. Humphrey and the team are baffled until they realise the fires follow an unusual pattern by invoking the Three Little Pigs fable. Meanwhile, Martha is in turmoil over what happened with Archie.

A house is burgled but the prime suspect was locked up in a police cell at the time. It's up to Esther to rally a devastated Humphrey and solve this impossible crime.