They are going to tour the prison on Raven Island. They are not enthused. There might be ghosts because the prisoners were never set free.
Viking Books for Young Readers and Edelweiss let me read tis book for review (thank you). It has been published and you can get a copy now.
There are ghosts as well as real people on the island. They take the tour and one of hem steals the previous warden's diary. That tells them of a secret and they sneak off the ferry and hide. They'll stay until the morning and see if they can find the secret.
Some of the ghosts are real people and there are ghosts that they thought were real people. What they are doing is dangerous and not everyone is their friend.
It's a busy book with action all through it. Do you think they'll find the secret?