Gray Hunter's Revenge

Frank and Joe investigate a supernatural crime in the seventeenth book in the thrilling Hardy Boys Adventures series.
One of the Hardys' favorite writers, Nathan Foxwood, has recently died in a tragic car accident. Now, the press is swarming his house in Bayport to get the scoop on the novel he completed just before his untimely death.
When Joe hears that Nathan's wife is having a giant estate sale, he drags Frank with him. Who could pass up the opportunity to see inside their favorite author's home? Nathan's wife says she wants to get away as quickly as possible; strange things have been happening since their first night there and now her husband is gone and she's sure the house is haunted. But Nathan's assistant, Adam, is not so willing to blame it all on the supernatural. Valuable things keep disappearing from the house—why would a ghost need money? Adam recognizes the Hardys' from an article he read and asks for their help.
Of course Frank and Joe Hardy don't believe in ghosts and are positive they can get to the bottom of all this. But when Adam is mysteriously hurt after spending the night alone in the house, the brothers start to wonder; what is the motive for these crimes if not ghostly revenge? Could these brother detectives be in over their heads?