While being ambushed by the Nosoi near Camp Half-Blood, Meg unknowingly summons a Karpos. He defeats the Nosoi by ripping them apart with his mouth. He repetitively says the phrase "Peaches", so Meg names him "Peaches". Percy Jackson attempts to kill him, but Meg pleads for him not to.
Meg tells Apollo that Nero took Peaches away from her saying that she didn't deserve a pet until she behaved. He first appears being tied high up above the ground during Commodus' naming ceremony rehearsal. The emperor plans to drive a race car with a giant match stick to burst Peaches into flames. Apollo saves him by having Livia the elephant knock over the car, Meg frees Peaches.
Apollo mentions Meg has not been able to summon Peaches since Indianapolis.
Peaches is seen in People’s Park in Berkeley. The local nature spirits explain that he has traveled from Palm Springs (despite not being seen there the previous book) to the Bay Area to inform them of what happened.
When Meg returns to Camp Half-Blood, he goes with her and her siblings to breakfast.
Peaches is seen at the end of the book, possibly flirting with Prickly Pear, another Karpos.
Peaches is aggressive and very protective of Meg.
Peaches is described as a "Demon Diaper Baby". He is also described as looking like a pudgy human baby toddler wearing only a linen diaper. He has green hair and eyes. He has sharp nails and dry, brittle wings like corn husks.
In The Tyrant's Tomb, his hair has started to brown and his wings have lost some of their leaves.
Peaches has the same abilities as any Karpoi.
- Enhanced Bite: His fanged mouth is so powerful he can even get rid of Nosoi.
- Flight: His wings permit flight.
- Backup Summoning: He has the ability to call for more Karpoi for help like he did with helping Meg in The Dark Prophecy after her experience in the Cave of Trophonius.
- According to Meg, Commodus is like Peaches to Nero, vicious but controllable pets.