Detective Looker's assistants Emma and Mimi have been helping him out in Lumiose City, until a crime wave threatens to tear them apart.
In the nightly alleyways of Lumiose City, a Trainer and her three Furfrou have been defeated by Essentia, a notorious Pokémon thief in a black suit and a face-covering helmet. As the Trainer recalls her fainted partners back into their Poké Balls, Essentia activates her suit's "Poké Ball Jack" function, remotely stealing the three Poké Balls straight from her opponent's hands. Just then, Looker arrives and orders her to stop at once. The Espurr accompanying Looker, nicknamed Mimi, approaches Essentia despite Looker's warnings and, to his surprise, starts affectionately rubbing itself against her leg. Essentia, however, suddenly proceeds to kick Mimi in the face, forcing Looker to catch it. The Pokémon thief then makes a huge leap and starts running away on rooftops, while Mimi starts floating after her, with Looker on its tail.
As the two pursue Essentia, Looker remembers the only person whom Mimi trusts that much, and stars wondering if the masked thief could in fact be Emma. Emma was an orphan girl with nowhere to go, so Looker took her under his care to work as his assistant at the Looker Bureau, where she's been of tremendous help. However, recently, she's been disappearing without letting Looker know. With this mind, Looker once again starts wondering if Essentia truly is actually Emma.
Essentia eventually runs into Lysandre Café, where Mimi and Looker corner her. Mimi glares at Essentia for a moment, before suddenly leaping and headbutting her face, cracking her helmet's screen. The helmet starts malfunctioning, until finally the person inside the suit screams and the screen shatters, revealing the person inside the suit to indeed be Emma. Looker catches Emma as she falls down. She opens her eyes and asks if today's experiment is already over. Looker asks Emma how did this happen, and Emma, upon recognizing them, responds by asking what he and Mimi are doing here.