13 Hangmen — Art Corriveau

"Some people won't believe any of this story. You might be one of them. But every single word is true. Tony DiMarco does catch a murderer, solve a mystery, and find a treasure -- all in the first few days after he moves, unexpectedly, to 13 Hangmen's Court in Boston. The fact that he also turns thirteen at the same time is not a coincidence."

So begins the story of Tony and his friends -- five 13-year-old boys, all of whom are living in the same house in the same attic bedroom but at different times in history! None are ghosts, all are flesh and blood, and somehow all have come together in the attic room, visible only to one another. And all are somehow linked to a murder, a mystery, and a treasure.