Marinette's class is having a field trip to London, but Marinette believes she cannot attend since doing so would leave Paris vulnerable to Hawk Moth. Master Fu gives her the Horse Miraculous, which grants the power of teleportation, so she can enjoy herself and be able to return to Paris in case of an emergency. Max's mother, a train conductor who directs the Startrain dreams of being an astronaut and has taken an exam to begin training. However, a rogue akuma gets aboard the train in Sabrina's big suitcase to London after a botched attempt to akumatize Officer Roger. When Max's mother succumbs to nerves waiting for confirmation about whether she passed, the akuma infects her and turns her into Startrain itself, and she drives the train into outer space. Since the akuma is outside of Hawk Moth's range of influence, Gabriel is forced to rely on the heroes to rescue Adrien. Ladybug gives Max the Horse Miraculous, turning him into the superhero "Pegasus". With his aid, the heroes teleport the train back to Earth, so Ladybug can safely purify the akuma. Afterwards, Max's mother gets the e-mail confirming she passed her exam, much to her delight.