User blog comment:Hermione Chase/"The Blood of Olympus" Expectations/@comment-10901795-20140814125303/@comment-5927468-20140815005629

While we didn't actually see him, Jupiter did help Jason beat Enceladus with a lightning bolt in TLH. So at least he got involved. And yeah, Poseidon's got to show this time.

I agree that Leo's oath to Calypso is definitely a red herring. Someone else mentioned that the "oath to keep with final breath"  might refer to Percy's promise that the Greeks meant no harm near the end of SoN. He swore on his life to the Romans, so that may well come up again.