With Fermín Romero de Torres now working at the Sempere bookshop, Daniel finds himself with unexpected free time. Fermín tirelessly organizes stock, polishes the shop, and hunts down rare requests, freeing Daniel to return to two priorities: pursuing the Julián Carax mystery and, more immediately, spending time with his best friend, Tomás Aguilar.

Daniel recounts how he first became friends with Tomás at their Jesuit school. After Daniel makes a tasteless remark about Tomás’s sister, Tomás—bigger and stronger—beats Daniel badly, knocking out a tooth, while Tomás’s father watches with pleasure. Weeks later, Tomás approaches Daniel to apologize, admits the fight was unfair, and shyly asks to be Daniel’s friend; Daniel accepts, and Tomás brings him home to show him strange homemade gadgets.

The friendship deepens as Tomás reveals himself to be gentle, solitary, and brilliant, though socially anxious and prone to stammering except when speaking Latin. Tomás becomes obsessed with mechanical devices, dismantling and inventing contraptions, and he grows attached to Daniel’s father, who encourages him with books and admiration—especially for Tomás’s long-running attempt to automate the shop’s index-card system.

When Daniel introduces Tomás to Fermín, Fermín treats Tomás with respect and humor, quickly drawing him into technical talk and carefully ignoring Tomás’s stammer. Fermín later tells Daniel that Tomás’s talent is real but that Tomás’s demeanor and intimidating appearance will make life difficult, and Fermín decides Tomás needs help developing social skills to survive a world ruled by prejudice.

Daniel then sketches Tomás’s home life: Mr. Aguilar, a prosperous property manager, looks down on his son and hires tutors, many of whom quit in frustration when Tomás answers only in fluent Latin. Daniel also describes Tomás’s sister, Beatriz (“Bea”), a privileged, stylish young woman Daniel dislikes and fears. Bea dates Pablo Cascos Buendía, a Falangist lieutenant who bullies Daniel and spouts nationalist claims, while Bea watches Daniel with an unreadable, unsettling interest.