Percy Jackson and The Half-Blood Protection...
Voldemort is alive, and growing stronger. The Ministry are ignoring Dumbledore's warnings and are making him out to be an old fool to discredit him. The Order of Phoenix are trying their best, but they aren't certain themselves. Harry Potter is losing his cool....and Albus Dumbledore is contacting Percy Jackson.
Dumbledore needs Percy...knows that Harry is the one destined to defeat Voldemort, but desperately needs help. So he asks Chiron, and Percy Jackson is sent to Hogwarts to protect Harry.