What Cerdic does is revealed to the reader in Chapter 10 of this exciting story. Having found Crispin at Peregrine's cottage, Cerdic pretends to have been sent by Father Quinel in order to give him advice. Cerdic initially accompanies Crispin, telling him to go towards the manor house in order to escape being caught by Aycliffe, the steward and his men. His role is to gently encourage him to go the way that Cerdic planned him to go, as it transpires that Cerdic is actually leading Crispin into a trap. As Crispin has been declared a wolf's head, money has been offered to anybody who can help detain him, and Cerdic is hoping to be able to earn the reward by leading Crispin into a trap. This is revealed when Crispin realises Cerdic has disappeared when a drum starts beating, revealing the presence of Aycliffe and his men:
There was still nothing to be seen, though the drum kept beating. Then I realised Cerdic had begun to back away from me. I turned to face the boundary cross again. This time I saw shadowy forms rise up from the side of the road. It was four men. They lumbered across the road, blocking my way.
What Cerdic does then is to betray his former friend, hoping to gain personal enrichment through leading Crispin into a trap where he can be captured by Aycliffe and then killed for his supposed "crime" of thieving from the manor house.