1. The Scale of the Conflict: The theft of Zeus' lightning bolt is a massive, audacious act. Ares, while powerful, wouldn't normally risk a war between the gods for a single weapon. This suggests he might have a higher power backing him up, someone with a greater stake in the conflict.
2. Ares's Motivation: Ares is driven by conflict and war. Stealing the lightning bolt, while a chaotic act, doesn't actually *cause* a war. This hints at a bigger objective, perhaps a desire to instigate a war between the gods. Ares might be working for someone who benefits from such chaos.
3. Ares's Deception: Ares initially claims to be innocent, even implying he is helping Percy. However, his actions and words contradict this claim. He is clearly manipulating Percy, suggesting he is part of a larger plan.
4. Luke's Involvement: Later in the book, Percy discovers Luke Castellan, a former camper, is working with the enemy. Luke's connection to Kronos, the Titan who wants to overthrow the Olympian gods, confirms that Ares is indeed part of a larger conspiracy.
5. The Prophecy: The prophecy concerning the son of Poseidon who would steal the lightning bolt is a major plot point. While Percy is the prophesied son of Poseidon, the theft itself points towards an orchestrated act, suggesting someone manipulated the prophecy to achieve their goals.
All these factors combine to create strong suspicion that Ares is not working alone. His actions, motivations, and connections all point towards a larger conspiracy involving the Titans and their desire to overthrow the Olympian gods.