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 to London in Sabrina's big suitcase after a botched attempt to akumatize Officer ...