SPOILERS for Secluded Cabin Sleeps Six by Lisa Unger

 

Mako's old secretary, Trina, the one who booked the house, was the killer. Joshua was another sibling. Their biological father was a sperm donor and a serial rapist and killer. Trina was trying to cleanse the gene pool. Bruce, Hannah's husband, was working with the FBI to bust Mako for all sorts of crimes.