Back cover summary:[1]

Haunted by evil!

Trick or treat has turned to terror for the Hardy Boys. Never before have they experiences a more horrific Halloween---a nightmare come true. First, it was Joe's friend Vanessa Bender...Then Frank's friend Callie Shaw...And now their own mother. Frank and Joe are the only witnesses to three shocking murders---and no one believes them!

Strange, unspeakable forces are loose in Bayport. Enemies the boys thought dead have risen like demons to taunt and terrorize them. Now they stand alone in a titanic battle against and awesome, unknown power---a chilling army of evil determined to pursue them into the grave...or to the very edge of madness!