The Justice League faces a new threat when the Fatal Five, a group of time-traveling supervillains, arrive on Earth. Tharok, Emerald Empress, Validus, Mano, and the Persuader seek to free their compatriot, the Legion of Super-Heroes member Braniac-5, who is imprisoned in the Green Lantern Corps' stasis cell. Their ultimate goal is to find the Green Lantern Jessica Cruz and persuade her to locate the time-travel technology they need for their nefarious purposes. The villains' arrival prompts the League to evaluate the threat level and strategize a response. In the process, they recruit new heroes, including the reluctant Cruz and Miss Martian, who must overcome her fears and hesitation to answer the call to heroism.

During the ensuing chaos of the Fatal Five's mission in both the present and future, the newest members of the Justice League struggle with their own personal battles. Miss Martian grapples with her desire to prove herself worthy of the team, while Jessica Cruz deals with the trauma of a past tragedy that interferes with her duties as a Green Lantern. Meanwhile, the veteran heroes – Batman, Superman, and Wonder Woman – work alongside the newcomers to stop the villains' plan from unraveling the fabric of time and preventing the catastrophic consequences that could result from the Fatal Five's success. The Justice League must find a way to come together, incorporating the strengths of each member, to thwart the Fatal Five's ambitions and safeguard the timeline.