Professor Layton and the Unwound Future
Celeste first appears walking down Flatstone Street in Future London. Layton notices her and is shocked by her presence, as she resembles his girlfriend Claire, and he has a flashback.
Later on, when Layton and Luke head to Chinatown, Layton sees Celeste walking ahead of them. He chases her around a corner, but she had slipped away. Layton then has a flashback, which explains that he had received his top hat from Claire.
Celeste doesn't appear again until Layton and co. enter Dimitri's research facility. When they are cornered by armed Family henchmen, she opens a hidden door and urges them to follow her, saving them. Here, she reveals herself as Celeste, Claire's little sister, who has been trying to solve the mystery of Claire's death. As the group decide to split up in order to escape, and she is escorted by Don Paolo, she leaves a cryptic hint for Layton as to where to meet next. The meeting place turns out to be at the Thames Arms.
At the Thames Arms, Celeste witnesses Layton and Dimitri's Puzzle Battle, and listens to them both as they explain the mystery.
Dimitri had been building a time machine with Bill Hawks ten years ago. Claire, whom Dimitri loved, was their lab assistant. The machine wasn't ready, but Bill had been offered a large amount of money to test it, and used Claire as the test subject behind Dimitri's back. The machine exploded, killing Claire and severely injuring Bill; the blast had been so powerful that it had also destroyed a nearby block of flats. Dimitri had been working ever since to rebuild the time machine to save Claire. Layton scolds Dimitri for his plans, then goes on to explain that the future London is not really Future London at all, but a huge set built in a cavern underneath the real London. He accuses the future Luke of building it, as if it wasn't the future London, why did he still think he was the future Luke? He turns out to be Clive, a man who lost his parents in the time machine accident and was bent on revenge. He runs off with Flora as hostage, and takes a speedboat to the lighthouse on the "Thames", which turns out to be the main control tower for a huge weapon; the Mobile Fortress.
Layton and Luke decide to somehow board the fortress by the Laytonmobile. Celeste insists that she go with them, but Layton refuses for her safety and drives off. Soon, Don Paolo lets Celeste also board the fortress via his flying machine.
After Layton and Luke rescue Flora and head to the surveillance room to see that the fortress has emerged in London, Celeste joins them, and tells them how they can stop Clive. They head to the generator room, where they find Bill Hawks wired up to the heart of the fortress. A hologram of Clive tells them that the fortress will explode if they remove Bill from the machine, so Celeste works with Layton to swap Bill's heartbeat for Claire's broken pocket watch, which Celeste had kept.
She and Layton also reversed the energy flow in the generator to prevent it attacking London, but start destroying itself. The watch gave them only ten minutes to escape, so they decided to somehow reach safety by the Laytonmobile.
Whilst trying to get off the fortress, Layton accidentally drives off it instead, but manages to save them all by pressing a switch that converted the Laytonmobile into a small aircraft. Don Paolo had installed the feature earlier in the game, telling Layton that "[It's their] ticket out of trouble."
Before landing, Celeste sees Clive in the control room unconscious. Feeling compassionate, she urges Layton to take her back so she can rescue him, and he eventually complies. When close enough, she jumps out onto the fortress, climbing into the control room and bringing Clive outside to wait for Layton to save them. He does just before the fortress falls back into the cavern, and explodes, completely obliterating the future London.