The Lost Island New York Review Children's Collection

Folks in young Michael Farrell’s town have been speculating about the lost island of Inishmanann for generations. Some say that the island is the last stronghold of the old god of the sea; others, that no on who has gone in search of it has returned to tell the tale. But everyone agrees that for a brave and enterprising spirit the island holds out the promise of things “rare and valuable.”
Four years ago, Michael’s father became obsessed with tracking down the elusive island.

He bought a fishing boat and set sail. No one has heard from him since. Then a shifty beggar turns up in town with a message for Michael Farrell: his father is on the island, and Michael must join him there.