Percy Jackson is in the middle of taking exams at school when Mrs. O'Leary (his dog) comes bursting into his class! Thank gosh he was already done taking his exam because we know how Percy does with getting kicked out of schools. 
 (view spoiler)[Thalia! I was so excited Percy got another encounter with the daughter of Zeus! Nico also gets thrown - literally - into the mix. Bringing the children of the big three together. (hide spoiler)] 
 Hades is having a problem in the underworld that only Percy and his gang are trusted to solve. The sword of Hades which can lock or unlock death has been stolen and Percy (and others) have been requested to return it.(view spoiler)[Ethan Nakamura, son of Nemesis, from the last novel who Percy saved but then he ran away to turn against them again stole the sword along with Iapetus (the titan). Iapetus falls in a river that erases memory though and is tricked into thinking his name is Bob and he's on Percy's side.(view spoiler)[ It's a really short story but still just as engaging and entertaining! We learn of some new enemies as well as learn of some traits of other Gods in the underworld. It was nice knowing what Percy experiences during the school year while he's away from camp a bit. (hide spoiler)] (hide spoiler)]