It's been months since Percy Jackson was literally ripped from his Uncle's fingertips, and taken away by HYDRA. Nobody knows where he is, nobody knows if he's even alive. The Avengers have been torn apart by the Accords, and are fighting their former teammates, losing sight of their goals.
Tony thinks they should sign the Accords, believing that it would give them more resources to try and find Percy and put a stop to HYDRA. He has his close friend Rhodey as War Machine, Natasha Romanoff as Black Widow, King T'Challa as the Black Panther, The Vision, and Peter Parker as Spiderman helping him.
Steve thinks that the Accords would just get in the way of trying to find Percy and HYDRA, not fully trusting S.H.I.E.L.D since it was revealed to be HYDRA. He has his long-time friend Bucky Barnes as the Winter Soldier, Clint Barton as Hawkeye, the daughter of his first-love Sharon Carter, his new friend Sam Wilson as Falcon, Scott Lang as Ant-Man, and Wanda Maximoff as the Scarlet Witch helping him.
As their battle seems to draw to an end, Tony and Steve battle it out in an abandoned HYDRA base. Then, something extraordinary happens.