One of the hundred books a year I read:

After his wife, Michelle, left seven years ago, Jeffy Coltrane does his best to raise his eleven-year-old daughter, Amity. Their quiet life is shattered when a genial homeless man leaves a package with them with the warning to hide it and never open it. When they accidentally activate it, they discover the device allows them to travel to alternate universes. As they search for the missing Michelle—or, at least, her alter ego—evil forces pursue them to steal the device. Unless Amity and Jeffy can outwit them, the place they call home may never be safe again.