Soon She Will be Gone by John Farris
Six women associated romantically with the ultra-rich architect Dix Trevellian have disappeared without trace. One of them was Dane Coleman's sister and he's sure that Trevellian is responsible. Coleman blackmails Sharon Norbeth, a beautiful young artist, to act as bait. He's sure that he can catch Trevellian in the act and avenge his sister, but once the pair is entangled in Trevellian's twisted web, it will not be long before Sharon will be gone.