In Percy Jackson and the Olympians: The Lightning Thief, who unknowingly had the master bolt and who had the helm of darkness? What were the master...

In Chapter 19, Percy meets with Hades in the Underworld. He addresses Hades as 'Lord and Uncle' and tells him that he has two requests to make of him.

Hades is not amused that the son of Poseidon has dared to make any requests of him, but he decides to humor Percy. Percy's first request is that Hades return Zeus' master bolt to him in order to prevent war between the gods. Before Percy can...

In Chapter 19, Percy meets with Hades in the Underworld. He addresses Hades as 'Lord and Uncle' and tells him that he has two requests to make of him.

Hades is not amused that the son of Poseidon has dared to make any requests of him, but he decides to humor Percy. Percy's first request is that Hades return Zeus' master bolt to him in order to prevent war between the gods. Before Percy can get to his second request, however, Hades accuses him of having stolen both Zeus' master bolt and his own helm of darkness. Hades threatens to release the dead back into the world unless Percy returns his helm. However, Percy denies that he has Hades' helm of darkness and demands Zeus' master bolt back instead.

In reality, Percy was tricked into carrying Zeus' master bolt in his backpack; in Chapter 20, we discover that Ares had given the backpack to Percy. When Percy accuses Ares of having stolen both the helm of darkness and the master bolt, Ares admits cryptically that he had both items stolen, but he didn't do the deed himself. It was Ares who actually disguised the master bolt's sheath to resemble a backpack; since the sheath is so powerful that the bolt always has to return to it, Ares tinkers with the magic so that the bolt will only return to its sheath (the backpack) when Percy entered the Underworld. This is how Percy came to unknowingly have the master bolt in his possession when he stood before Hades.

Meanwhile, Ares has in his possession the helm of darkness. It is disguised as a ski cap,' the kind bank robbers wear.' When Ares deposits the ski cap between the handlebars of his bike, the cap immediately turns into a bronze war helmet. The chapter ends with Percy, the son of Poseidon, defeating Ares in battle. After changing into his immortal form, Ares vacates the scene of the battle and leaves the helm of darkness behind. Percy charges the Furies with returning the helm of darkness to Hades in the Underworld.