Thread Of Revenge by Elizabeth Goddard

Coast guard protector!

Marine biologist Sadie Strand is back in her coastal hometown to prove her best friend was murdered – but searching for evidence almost costs Sadie her life. Abducted, drugged and left for dead on a sinking boat, she's barely rescued in time by Coast Guard Investigative Service special agent Gage Sessions, an old friend. Assigned to protect Sadie and connect three complicated cases, Gage risks his life time and again to make sure the woman he once loved survives. But although the handsome, guarded agent vows to protect her, someone will keep killing to ensure the truth never rises to the surface.