Undercurrents by Laurel Mills

Photograhper Marha Felkins returns for the summer to the rugged Maine Island where she grew up. It has been nine months since her companion Grace died here in a strange accident on THE SYBIL, a lobster boat captained by Martha's brother. Martha has come back, hoping that being near her brother and his grown retarded son will help her heal from grief. Instead, she uncovers the shocking secret behind Grace's fatal accident, even the island doctor, Sue Whitaker, doesn't know.