Layton Brothers: Mystery Room

Arriving at Scotland Yard on her first day, detective constable Lucy Baker is advised by the Commissioner and his Deputy of her posting to a department of the Serious Crime Division nicknamed the "Mystery Room" as assistant to inspector Alfendi Layton, an apparent genius investigator. Upon their meeting, Alfendi has Lucy work alongside him to solve the murder of a young woman at a seaside resort as a test. Managing to prove herself, the pair begin work together in earnest, solving a new case involving the death of a stay-at-home husband. During their inquiries, Lucy discovers that Alfendi has a "split personality", encountering his "deranged persona" for the first time in the middle of a climactic interrogation.

After investigating the public shooting of a popular stage actress at the request of Alfendi's old partner, Justin Lawson, the duo set about examining a new case, an alleged "supernatural" locked room murder of an archaeologist in South America, who was rumored to have been the target of the curse of a (now stolen) stone idol he had uncovered. They discover that the killer is actually Chico Careta, a local guide, and that he was manipulated into the crime, and used as a scapegoat, by his fiancée, Mariana Etista. Reasoning that, upon discovering that Scotland Yard were reopening the case, she sent Chico to England to take the fall, the pair are forced to defer the case's closure so long as she remains on the run. A further slaying, that of a popular DJ at a radio station, also successfully resolved, the pair receive a personal request from the Commissioner to look into the deaths of a group of mafia members. The manner of their deaths all seem to be copycat murders based on the "Jigsaw Puzzle Killings", a 26 victim serial killing from four years ago that was never made public knowledge. Alfendi and Lucy ultimately deduce that one of the mafia members killed the others alongside an unknown female accomplice, only to be betrayed by her and himself killed.

Some time later, Alfendi is alerted by Hilda Pertinax, an Interpol investigator he has history with, that Mariana Etista's whereabouts have been traced to a safe house in England. Upon uncovering Mariana's hiding place, it is revealed that her true identity is that of Diane Makepeace, the daughter of the Jigsaw Puzzle serial killer, Keelan Makepeace, who has followed in her father's footsteps and become an equally brutal murderer. She reveals herself as the one who orchestrated the mafia murders, and expresses a deep hatred for Alfendi, accusing him of "murdering" her father during a confrontation four years ago.

Diane manages to escape, and sends an invitation to Alfendi to visit Forbodium Castle, where Al and her father had their fateful showdown four years ago. Arriving in pursuit of Alfendi, Lucy and Hilda are separated, and Lucy is locked in a room by Diane, who forces her to solve a reenactment of a murder in order to escape. Upon solving it, Diane tells Lucy that this was her father's first killing; Keelan had once told her he had help inside the police, someone who destroyed vital evidence in that particular case. Lucy is shocked to discover the investigator in charge of the case was Alfendi.

As Lucy makes her way deeper into the castle, a gunshot rings out, and she and Hilda arrive on the scene to find Diane has been fatally shot, with Alfendi, who was being held captive by her, the only plausible culprit. Despite this, his "Potty Prof" personality asserts that the one who killed Diane is the same person that killed her father four years ago, proclaiming his own innocence in both slayings. He asserts that Hilda, Justin Lawson, and Commissioner Barton are all to be considered suspects, as they were the only people involved in the Forbodium Castle incident four years ago.

Upon investigation of the two incidents by the trio and a newly arrived Justin, the impossibility of a culprit other than Alfendi appears irrefutable, and, despite every new fact brought to light, Lucy is gutted when the "Placid Prof" asserts his own guilt. Despairing, Lucy is told by Hilda that "Potty Prof" is actually the Alfendi she and Lawson worked alongside, and that his gentle, "normal" personality is the so-called "fake one" that formed four years ago. In spite of this shock, Lucy resolves to keep believing in Alfendi, and conducts a final investigation, through which she unveils Justin as the mastermind behind the murders of Keelan and Diana Makepeace. He had found out about Keelan being the Jigsaw Puzzle Killer four years ago, and made him a deal, allowing him his liberty so long as he eliminated certain people at Lawson's request. He also took advantage of the Jigsaw Puzzle Killings to disguise other unrelated murders, placing jigsaw pieces at their crime scenes. Lawson killed Keelan to silence him, and killed Diane out of a fear that questions about the incident were resurfacing, especially surrounding the increasingly frequent fronting of "Potty Prof". However, even after confessing, he refuses to elaborate on his original motives, simply stating that some bad people had become too powerful.

Some time later, Alfendi visits an incarcerated Justin, who claims that the origins of Alfendi's "placid personality" are in brainwashing efforts made on Al by Lawson while he was in a coma following the Forbodium incident, in the hope of ensuring Al kept his mouth shut. Both of Alfendi's personalities and Lucy are all unconvinced that such a cheap trick could work, and vow that between the "three of them" they'll solve the "mystery of Placid Prof". In a final scene, the Commissioner is seen talking on the phone about recent events with an old friend named Hershel.