The Son of Neptune (Heroes of Olympus, Book 2)

The first book in the Heroes series had Jason with the Greeks. This one has Percy Jackson hanging out with the Romans in San Francisco. He has some memory loss, but it was not as bad as Jason's in the first book. He teams with some Roman demigods (including a reluctant son of Mars) to go on a quest. They are treated as relative outcasts by the Romans who are already into their bureaucratic ways. They manage some trickery of luring a giant out of Alaska so as to defeat him outside his home turf. Like usual, there is plenty of action and end-of-the-world situations.