Comparison:
The Lightning Thief strongly resembles one of the other books he wrote, The Lost Hero. The Lost Hero is about 3 kids, two boys and one girl. One of the boys is a past failure and is trying to prove himself worthy (just like Grover), the other boy is the son of one of the big three in the Roman Gods context (just like Percy), and the last one is itching for a quest (just like Annabeth). They are both sent on quests and have everything play out very similarly to The Lightning thief; its almost as if he took The Lightning Thief and translated it to a Roman gods version of the story. They are different, though, in the way that they are all sent on there quests for different reasons, and they all fight different hardships than the greek heroes of Percy, Grover, and Annabeth. And also, the roman heroes fight much different monsters than the greek heroes did in The Lightning Thief.