|“||Oh, I like the way you think. They sent me because I excel at messing things up.||”|
Cecil first appears when Nico di Angelo leaves the Romans Leila and Dakota, shadow traveling to the crest of Half-Blood Hill next to Thalia's Pine Tree where Will Solace, Lou Ellen, and Cecil where scouting the enemy. Nico at first does not see Cecil and the others as he is focused on studying the Romans following Octavian when Will makes there presence known. Nico does not recognize Cecil or Lou Ellen until Will introduces him as a demigod from the Hermes cabin. As Nico argues with Will about using his powers, it is noted that both Cecil and Lou Ellen look back and forth between the two as if "they were watching a really intense tennis match." Cecil states that he brought some Greek fire, but Nico vetoes his idea and instead asks Cecil if the son of Hermes could re-calibrate the aim of the onagers toward the other firing lines. Cecil grins at this and comments that that's why they sent him there because he's great at messing things up. Cecil works on each onager while the other demigods guard him in case any Romans suspect or notice anything over the Mist from Lou's magic. While heading toward the third machine, they are noticed and Nico uses his powers to bring up skeleton warriors to fight the Romans. Cecil joins in this fight while Will fusses over Nico. After the small fight, Cecil comes back limping, looking like he had pulled a muscle and points out to the two arguing demigod that they had missed the fight. During all the bickering, the Romans, Octavian, and the cynocephali came up. After Reyna brings the Athena Parthenos back to the Greeks and Gaea awakening, he presumably fought monsters and helped free the Romans.
Cecil is one of the campers to vanish when the Grove of Dodona was threatened by Nero. He was eventually freed by Austin Lake and when he, Apollo and the other captives flew back to camp on female Myrmekes and distracted Nero's automation.