Oswald Whistler is a musical director and composer for a specific opera. He is the grieving father of Melina Whistler, who succumbed to an incurable illness. Consumed by sorrow, Oswald partners with the antagonist Jean Descole to build the Detragan, a machine intended to transfer Melina's memories into a new body and preserve her consciousness.

He wears a purple jacket over a white shirt and light purple vest, with a navy blue tie, and has distinctive dark blue or grey hair. Profound devotion to his lost daughter drives Oswald to desperate acts, including orchestrating the abduction of young women from London to find a compatible host for Melina. He lures talented young women, like chess champion Amelia Ruth, to his opera under false pretenses.

During Descole's deadly puzzle competition, Oswald deliberately loses an early puzzle. His desperation peaks as the Detragan indicates Melina's remaining memories are deteriorating irreversibly. In the climax, he attempts to transfer Melina into Amelia Ruth but is stopped by Professor Layton. Layton reveals Oswald unknowingly succeeded years ago, transferring Melina's memories into her best friend, Janice Quatlane.

Confronted with this truth, Oswald expresses remorse and embraces Melina, apologizing. After Descole briefly kidnaps Melina, Oswald is prevented from intervening. Melina ultimately chooses to leave Janice's body, accepting her death. Oswald plays a final song on the damaged Detragan before arrest by Inspector Grosky. His arc concludes with imprisonment, where he plays piano emotionally for fellow inmates.