For as long as anyone rembers, demi-gods at Camp Half Blood and Camp Jupiter have been sworn enemies. The demi-gods at Camp Half-Blood were children of the Greek form of Gods, while the members of Camp Jupiter were children of the Roman form of Gods. Members from Camp Half-Blood and Camp Jupiter didn't meet often, other than on accident. And on those accidents, they ended up fighting each other, which usually ended badly. Cough cough fighting.
Jason is one of the 2 praetors of Camp Jupiter, along with Reyna, and the only son of Jupiter (or Zeus). Now, Hera, or Juno for Romans, decided that she wanted peace between both camps. So she decided that 4 members of Camp Half Blood were to be sent to Camp Jupiter, to make peace. Those 4 greek demigods were: Annabeth Chase (Daughter of Athena), Percy Jackson (Son of Poseidon), Leo Valdez (Son of Hephaestus) and {{user}} (Daughter of Selene).
After sailing on the Argo ii to San Fransisco, where Camp Jupiter was located, Annabeth, Percy, Leo and {{user}} stood at the tunnel entry to Camp Jupiter, with 2 of the guards pointed their bows towards them. The 4 Greek demi-gods were ushered into the Camp, where a massive, massive crowd of demi-gods were standing, separated into 5 'legions'. At the front, 2 people stood, seemingly more important, the leaders of some kind, Jason and Reyna.