Whilst posing as a pilot for General Erich Ludendorff, Steve Trevor discovered that Ludendorff's chief scientist - Dr. Isabel Maru - was developing a deadly weapon that could change the outcome of the war in Germany's favor. Knowing that he could not stand by and allow millions of innocents to die at the hands of this weapon, Trevor stole Maru's notebook and exposed himself as a spy to the Germans. Stealing a plane, Trevor managed to escape from the Ottoman Empire base where Dr. Maru was developing her deadly gas.
Trevor's plane crashed in the water surrounding the island of Themyscira, where he was rescued by Princess Diana and brought to the shore. However, the Germans were still actively pursuing Trevor, and in doing so, breached the magical barrier that cloaked Themyscira from the outside world.
As the Germans made their way to the shores of Themyscira, the Amazons arrived and drew first blood. As the two sides engaged in battle, a German soldier took aim at Diana with his gun and attempted to shoot her. Before he could pull the trigger, Diana's aunt and general of the Amazons, Antiope, intercepted the bullet and sacrificed her own life to save Diana's. Steve Trevor killed the soldier before rushing to Diana's side as Antiope muttered her dying words.
After the battle's conclusion, several Amazons called for the death of Trevor, believing him to have brought the Germans to their island. Diana defended Trevor from her fellow Amazons, saying that he fought at her side. However, Trevor refused to answer any questions about his identity and intentions, prompting the Amazons to use the Lasso of Hestia to gain answers. Through interrogating Trevor, the Amazons learned that a great war was being waged by mankind, the likes of which Trevor has never seen before. This revelation was what convinced Diana that the God of War, Ares, was the one responsible for orchestrating the war. Armed with gifts from the gods, Diana set off into the outside world with Trevor with the task of defeating Ares and the war.