I Found You by Lisa Jewell

When Alice sees a man sitting on the beach all day outside her home, she begins to worry. After talking to him, she realizes he's lost his memory and has no idea who he is. While in London, newlywed Lily fears her husband, Carl is missing after he doesn't come home from work. In an alternate storyline set in 1993, the Ross family arrives at the cottage they rent every summer in Ridinghouse Bay in East Yorkshire. Teenager Kirsty meets a man named Mark whom her older brother, Gray, takes an immediate dislike to. It soon becomes clear that all is not right with Mark and his feelings for Kirsty. I Found You explores the lives of Alice, Lily, and the Ross family, with the reader wondering how the storylines will intersect.