The Dark Mirror

Dr. Frank Peralta is stabbed to death in his apartment late one night. Two witnesses quickly place Terry Collins at the scene, casting suspicion on her from the start. Lt. Stevenson launches a thorough investigation, gathering statements and reviewing Peralta's connections.

Despite the witness accounts, Terry's alibi is airtight, supported by several additional witnesses. The police and the district attorney are unable to prosecute without a clearer link to the crime. The case stalls as investigators debate whether the 'perfect crime' could actually be possible.

Investigators learn Terry and Ruth are identical twins who share a job and routinely swap places for personal gain. This twin-switch explains why any single suspect could look innocent despite the murdered man's death. The team realizes proving who was at Peralta's apartment will be essential and difficult.

Lt. Stevenson asks Dr. Scott Elliot, an expert on twin studies, to help identify which sister is which. Scott proposes studying the twins separately under the guise of research to isolate their true personalities. Terry and Ruth agree to participate, though Ruth worries about the risk of discovery.

Scott's tests reveal clear personality differences: Ruth is kind and loving, while Terry is highly intelligent and unstable. He also uncovers Terry's long-running manipulation of Ruth and her jealousy of being eclipsed by her sister. Scott reports these findings to Stevenson to guide the next steps.

Terry's jealousy drives her to escalate the conflict, exploiting Ruth's trust and manipulating her into believing she is losing her grip. She uses psychological pressure to push Ruth toward instability, all while maintaining control over her own image. The sisters' dangerous dynamic grows more volatile as the plan unfolds.

Scott advises Stevenson to warn Ruth immediately about the danger posed by Terry. Stevenson weighs the risk but decides to proceed with caution, aiming to protect Ruth without tipping off Terry. The warning plants seeds of suspense as everyone awaits the inevitable confrontation.

Scott arranges a meeting with Ruth at his apartment to discuss their research, but Terry intercepts the plan to maintain her cover. Her interference keeps Ruth in the dark about the true danger facing her. The maneuver demonstrates Terry's reach and willingness to manipulate everyone around her.

Terry leaves Ruth alone in their apartment and hides a music box to encourage Ruth to believe she is developing madness. The device becomes a tool in Terry's psychological warfare, blurring reality for Ruth. The scheme escalates the danger and stakes for the twins.

Terry confronts Scott at his apartment, and he believes he is speaking with Ruth. He outlines the twins' rivalry and the motive for Peralta's murder, not realizing he is actually talking to Terry. The revelation confirms to Terry that she can manipulate the situation to her advantage.

Stevenson goes to the twins' apartment on a hunch and pretends to have called Ruth, prompting Terry to maintain her deception. He stages events to test Ruth's wellbeing while keeping the public face of the investigation calm. The trap sets the stage for a crucial confrontation.

At the twins' apartment, Terry pretends that her sister killed Peralta and died by suicide, while claiming to be Ruth. Ruth arrives alive, exposing Terry's ruse, and a heated moment ends with Terry throwing a glass at a mirror showing Ruth's image. Stevenson arrests Terry as the deception collapses.

Stevenson reveals that he had previously visited Ruth and found her distressed, not dead, then staged a phone call to trap Terry. With Terry in custody, Ruth is cleared and free to pursue a life with Scott. The case closes on a note of reconciliation and a cautious optimism about the twins' future.