“Faithfully Yours” opens with a little teaser: A dog trots out of a beach house garden to greet its owner and leaves bloody paw prints on his nice white shirt. After that, we’re introduced to Bodil Backer (Bracha von Doesburgh), a court judge and mother who is married to Milan (Nasrdin Dchar). They seem happy enough, but she can’t wait for her girls’ trip to the coast with best friend Isabel (Elise Schaap), who has planned a weekend of lectures and historic walks. Soaking up the local culture is the last thing on their minds, however; they use these jaunts to cover up each other’s extramarital flings.
They are meant to be staying together in Bodil’s gorgeous beach house, but Isabel leaves her phone and checks into a grand old hotel instead. While Bodil dutifully attends a lecture to get snaps to supposedly prove where Isabel is, her friend is heading off to a club instead. Meanwhile, Bodil meets Michael (Matteo Simoni), the dishy lecturer, and spends the night with him.
Isabel has to return home after her novelist husband Luuk (Gijs Naber) breaks his ankle, leaving Bodil alone to enjoy the rest of the weekend. Michael wants to hang out but she makes it clear that she was only interested in a one-night stand. Returning to the beach house after a swim, she discovers signs of a break-in and a pool of blood on the floor. The cops determine that it belongs to Isabel and question Bodil, who unwisely lies to cover herself and her friend’s infidelities. It’s a bad idea because when Isabel’s second phone shows up with a photo of her murder and Michael refuses to corroborate her alibi, she becomes a suspect. Worse still, Milan shows up with Luuk and starts acting suspiciously.