What does Percy discover about his father?

In chapter 3 they drive out to Montauk, and both Percy and his mother are extremely happy to be there—it was where his mother met his father. She tells Percy his father would be so proud of him, and they talk about him. His mother reveals that she will have to send Percy away to a summer camp keep him safe, because it is not safe for him to be close to her anymore. She does not explain further.