Marcus is 11 when his mom is killed in a car accident, and with no other known family, he is sent to love with his great-aunt Charlotte. She's had plenty of time to settle into her solitary routines, and Marcus is always aware that he's interrupted them. So he tries to make himself scarce and let her focus on her art, and part of his routine involves biking to the Grief Cottage at the northern end of the island--and sometimes making contact with the ghost of a teenage boy. 
 The ghost is really an afterthought to the story, which is a quiet exploration of loss and grief and forging of new families. (Aunt Charlotte, FTR, does not give much impression of disliking Marcus; he's just aware of being in her space.) Marcus is grieving his mother while acknowledging how much her death has improved his situation, lifting him out of poverty and giving him a father-figure he'd never otherwise have--a tricky thing for anyone to deal with, much less a young boy. 
 Marcus's voice is that of an adult looking back (and in fact this is the case, near the novel's conclusion) instead of a genuine 11-year-old, though he is clearly very smart and precocious in ways that only come from spending most of one's childhood around adults. 
 Well-developed characters and exploration of themes, and while the supernatural elements made SENSE they weren't prominent enough in the narrative to really call this a ghost story.