Numerius comes into contact with Spartacus for the first time while Batiatus is buying armor for the gladiator, and is fascinated by him and his triumph over Theokoles. Spartacus invites Numerius to the villa with the intention of practicing with him, but his desire is to steal the Thracian knife that Numerius had bought that day. Later, the two duel in the villa assisted by Batiatus and Titus Calavius. When Numerius leaves, Spartacus pockets the knife from his belt and Numerius doesn't seem to notice.
On his 15th birthday, the party is held in Ludus Batiatus, of his own free will. While there, he trains with Spartacus and enjoys time with his friends. He pauses in the baths and is approached by Ilithyia, who seduces him. When the display of the gladiators arrives, Numerius asks Spartacus to fight Varro instead of Crixus (having been convinced by Ilithyia); Batiatus fulfills his wishes, since it is his birthday. However, when the battle comes to an end and Numerius is called a prank to decide his fate, he decides that Varro must die. Horrified and dismayed, Batiatus claims that this was only a demonstration, but he feels forced to make Spartacus obey so as not to disturb Numerius' father, Titus Calavius.