Percy's mother Sally has a past that haunts her. She may have left her old life behind but that doesn't mean that it won't come searching. Sally was childhood friends with Natasha Romanoff who decides to pay Sally a visit successfully involving Percy in more than he signed up for (as usual).
Takes place after The Blood of Olympus and before The Avengers.
I don't own any of Rick Riordan's creations, nor any Marvel ones. I also don't own the image used for the cover.