Janie and John disagree on how to investigate the untimely death of the best man, Gethin Bennion. Janie suspects the bride Sioned or the groom's brother, while John goes against Janie's wishes and befriends the bride to gain insight into the wedding party, leading to tension between their investigative approaches.

Janie is forced to confront her own experience of a friendship turned sour in order to connect with a suspect and crack the case, revealing emotional depth behind her investigative work.

John forms an unlikely connection with one of the suspects over art and painting, which causes him to re-evaluate the role that work played in his own marriage and the circumstances around his late wife's passing.

It is revealed that the best man, Gethin, was having an affair with the bride, Sioned, which is the secret that led to his death and shocks the wedding guests.

The investigation uncovers complicated family dynamics and betrayed friendships, showing how far people will go for love, including suspicion shifting among the bride, the groom's brother, and the groom himself due to affairs and overlooked roles in the wedding party.