Lincoln and the Louds are ecstatic to welcome their new Gran-Gran, Myrtle, into the family with a tropical wedding celebration; but the festivities are cut short when an old nemesis from Myrtle's secret agent past appears on the island.
In the near future, a weary Logan cares for an ailing Professor X in a hideout on the Mexican border. But Logan's attempts to hide from the world and his legacy are upended when a young mutant arrives, pursued by dark forces.