You Belong to Me by Mary Higgins Clark

The one he had chosen was seated at a window table across the panelled dining room of the Gabrielle, a luxury liner that was the perfect size for his purposes. When he had spotted her sitting wistfully and alone at the table, and later had witnessed her tremulous, almost girlish pleasure when one of the male hosts asked her to dance, he knew right away how easy it was going to be.
   He raised his glass, and with the faintest movement in her direction, offered a silent toast.
   Your prayers have been answered, Regina, he promised. From now on, you belong to me.

A killer who targets lonely women on cruise ships is at the centre of Mary Higgins Clark's newest thriller You Belong to Me, a masterful combination of page-turning suspense and classic mystery.
   When Dr. Susan Chandler decides to use her daily radio talk show to explore the phenomenon of women who disappear and are later found to have become victims of killers who prey on the lonely and insecure, she has no idea that she is exposing herself--and those closest to her--to the very terror that she hopes to warn others against.
   Susan sets out to determine who is responsible for an attempt on the life of a woman who called in to the show offering information on the mysterious disappearance from a cruise ship, years before, of Regina Clausen, a wealthy investment adviser. Soon Susan finds herself in a race against time, for not only does the killer stalk these lonely women, but he seems intent on eliminating anyone who can possibly further Susan's investigation.
   As her search intensifies, Susan finds herself confronted with the realisation that one of the men who have become important figures in her life might actually be the killer. And as she gets closer to uncovering the identity, she realises almost too late that the hunter has become the hunted, and that she herself is marked for murder.