Even though Kevin has evidenced 23 personalities to his trusted psychiatrist, Dr. Fletcher, there remains one still submerged who is set to materialize and dominate all the others. Compelled to abduct three teenage girls led by the willful, observant Casey, Kevin reaches a war for survival among all of those contained within him, as well as everyone around him, as the walls between his compartments shatter apart.

After the conclusion of the film Split, David Dunn pursues the Beast, which is Kevin Crumb's superhuman personality. The encounters with the Beast escalate as Elijah Price materializes as an orchestrator who knows critical secrets about both Dunn and Crumb.

In the 1930s, three friends witness a murder, are framed for it, and uncover one of the most outrageous plots in American history.