A Commotion on the Ocean

Mystery writer Ashley Calloway's long-awaited vacation on a cruise ship isn't off to a flying start.  Delphina Durand, the worst former co-worker Ashley ever knew when she worked at Grandscale Pictures Corporation, turns out to be onboard, and she's just as crazy and vicious as ever.  By coincidence, Ashley's former boss, Preston, also turns out to be on the ship, along with his wife, Lorelei, who promptly goes missing - while the ship is at sea!  Delphina had stalked Preston when they all worked together way back when, so it looks entirely possible like she had something to do with his wife's disappearance.
 The prevailing theory is that she pushed poor Lorelei overboard. Did Delphina have something to do with this?  Can Ashley figure out what's going on here?  And where's Lorelei?