The following version of this book was used to create the guide: Silvera, Adam. Infinity Son. HarperCollins Publishers, 2020.

In Infinity Son, brothers Emil and Brighton are thrilled to turn 18. Their block party celebration, however, is disrupted when Spell Walkers, Maribelle and Atlas cause a riot chasing a specter woman through the street. The event makes Emil consider the dangers of having powers at all, while the night makes Brighton crave fame and power.

The next day, the boys attend a rally at the park, where they witness two boys fighting with powers. Their third friend, Orton, a specter, scoffs at them. He says they are only drinking a potion that gives them the illusion of having powers. Brighton wants an interview with them for his online videography series, but Emil drags him away. On the train, Orton and his friends reappear and start a fight. During the battle, Emil realizes he has phoenix powers.

After his hospital recovery, Emil is taken into the care of the Spell Walkers at their headquarters. When Maribelle, Atlas, and their companions, Iris and Eva, probe the boy's mother, Carolina, for more information, she reveals the truth: Emil is adopted. Her late husband found him abandoned in the street on the night Brighton was born. Because they feared his lineage, they kept the truth from him to give him a normal life. Emil is upset, but Brighton reminds him they are still brothers.

Eventually the Spell Walkers determine that Emil is the reincarnation of evil specter Bautista de León, and, therefore, the Infinity Son. The news shocks everyone, particularly confusing Emil. He is afraid of what he might do with his powers, and wants to stay true to himself. With the help of his friends, family, and the Spell Walkers, Emil decides to embrace his destiny and join the Spell Walkers' efforts to defeat their evil opponent, Luna Marnette and her band of Blood Casters. The Spell Walkers spend many hours training Emil. Meanwhile, Brighton grows increasingly jealous, wishing he were the one with all the power and attention. He begins posting endless videos of his brother online, and works to win the favor of the other Spell Walkers.

Believing Orton can give them needed information on Luna's activities, the Spell Walkers plan a battle between Orton and Emil. During the battle, Orton is killed. Emil is plagued by guilt, though it was not his fault. He does not feel like himself, and fears his capabilities.

Not long later, Maribelle and Atlas encounter a figure near the marina, who tells them Luna is planning to attack the Apollo Arena and kidnap the hydra for her new potion. During the arena battle, the same figure returns, morphing between bodies. Everyone realizes this individual, known as Ness, is really the evil Senator Iron's supposedly dead son, Eduardo. The Spell Walkers capture him and hold him at their headquarters. During his stay, he and Emil become close. The two trust one another and become intimate. Ness even reveals Luna's plans to make an immortality elixir to forever prevent her death.

They work together to attack Luna and her followers at the cemetery where she is capturing her parents' ghosts, another element she needs for the elixir. During the fight, Emil seizes the ghost urn and flies away. Everyone makes it back safely, except for Brighton. Emil eventually convinces everyone to rescue his brother, despite the obvious risk. They promise Luna the ghosts in exchange for Brighton. However, during the planned tradeoff, Ness betrays Emil. Brighton makes it free, but Emil is captured by Luna. Seeing Emil's shock and hurt, Ness curses himself.

After a long captivity, the Blood Casters bring Emil to the museum to capture the coveted Gravesend phoenix egg. The Spell Walkers appear and another battle ensues. Ness switches sides, determined to make up for his wrongs against Emil. He saves his friend and rescues the egg.

In the days following, the Spell Walkers develop a plan to stop Luna once and for all. During their final battle, however, Luna succeeds in killing both Gravesend and her parents' ghosts. She uses their blood to make the Reaper's Blood Elixir. While the others keep her from drinking it, Brighton seizes the vial and drinks it himself.