Will and Leonard witness a deadly and deliberate hit-and-run in Grantchester. Geordie traces the car to a pair of decidedly dysfunctional brothers whose house lies far off the beaten path. The victim's wife, his employee and the two brothers are all damaged characters caught in a web of lies and betrayals, and it's not just secrets that are hiding within the brothers' grounds.

When a young man is found dead and stark naked out on the Fens, Will and Geordie discover ties to a Cambridge research project experimenting with mind altering drugs. 

As the case gets murkier, Will's own feelings of guilt about his father's death and his conflicted feelings about Ellie start to take their toll. Is he prepared to delve deep within himself to find the answers? With everything else in his life seemingly in the pits, he'll need the help of his friends to figure this one out.

Similarly, the Keatings face one of their toughest decisions yet, after a catastrophically awkward dinner party leaves more than just the baked alaska burnt around the edges. Will Cathy finally tell Geordie the truth about her mother?

And with the Chapman feud showing no sign of relenting, Leonard must try to convince Mrs C that there's good in the world, but will the most wilful woman in the parish ever come round?