The Drowning Sea by Sarah Stewart Taylor

After leaving the police force on Long Island, Maggie D'arcy is contemplating a move with her teenage daughter Lily to Dublin to live with her boyfriend Colin and his son Adrien. The four are spending the summer in West Cork in a remote cottage when human remains wash up on the beach. The body is identified as Lukas Adamik, a Polish construction worker who disappeared months ago. Soon, Maggie finds herself immersed in the investigation-- interviewing local residents, and pondering if Lukas' murder is connected to drug smuggling in the area or even mysterious goings-on at Rosscliffe House many decades ago. Will Maggie's questions put herself and those close to her in danger?