The Hunt for the Seventh by Christine Morton-Shaw
Back into my suspense/scary mode. This was pretty good...Jim, along with his sister Sal, and their father, move to Minerva Hall. Dad has taken a head gardening job to help put their lives back together after Mom passed away. Until dead kiddos start appearing to Jim, begging him to find the seventh. A long time summer solstice mystery pops up, with a Minerva heir dying tragically, a total of 6 have died, and Jim is on the hunt for the seventh.
(from jacket cover)
A haunted mansion. Six Dead Children.
A garden of statues.
With every step he takes around the carefully manicured grounds of Minerva Hall, Jim is haunted by the ghosts of children, long dead, whom no one else can see. Urging him to "find the Seventh," the children leave him cryptic clues pointing to a devastating ancient prophecy that only he can stop from being fulfilled.
Jim befriends another boy-Einstein, who lives at the Hall. Einstein is autistic and very, very smart. If anyone can help Jim find the Seventh, perhaps he can-Einstein clearly knows more than he is saying. At the same time, the dead children seem to be leaving Jim some sort of macabre treasure trail.
If Jim deons't figure out the clues, innocent people will die. But how can Jim find the answers while the dangers of the Hall grow ever more threatening? And even if he can, the reall question is-is Jim already too late?