Houdini is a skeptic determined to prove the supernatural world to be a lie. Doyle searches for something greater than the world around us. Can they work together to solve a murder supposedly committed by a ghost?
Winnie, a nun, hears a baby’s cry coming from Sister Fabien’s quarters. She investigates and finds the sister’s throat slit. She sees a specter go through the wall above her.
A detective interviews Winnie. She tells him Lucy killed Sister Fabien. Sister Mathilda tells the officer she’s confused. Lucy died 6 months ago.
Houdini and Doyle meet up at Scotland Yard. Houdini bets Doyle $10,000 that he can’t prove the supernatural is real. The head policeman says they’ll be allowed to investigate if they take one of his officers. He thinks it’s funny to offer them a woman named Constable Stratton.
Stratton explains that the convent takes in unwed mothers in exchange for work in the laundry. Sister Grace greets them at the gates. They walk through the laundry room. All the women look worked to the bone. Grace says some of the girls have been seeing Lucy for months.
Both sets of keys for Fabien’s office were accounted for. Houdini picks the lock showing the killer didn’t need keys. Sister Mathilda has nasty things to say about Lucy. Houdini tricks her into leaving the room and then asks Winnie why she’s lying. She sticks to her story.
Stratton asks why Lucy would have killed Fabien. Winnie says Fabien murdered Lucy. Fabien took Lucy’s baby away and when she became distraught, Fabien cut off her hair and locked her out undressed in the rain. Lucy died two days later and was buried in an unmarked grave.
Houdini suggests the murder was a robbery gone badly. He asks where the money is that the laundry takes in. Winnie pulls out a box, but it’s empty.
Doyle goes to a questionable medium. She tells him a man of soot committed the crime. She says he’s in Whitechapel telling his exploits to a rabbit. She asks what the real reason is Doyle came to see her. He asks her to contact his wife. She suddenly supposedly comes through and tells him he’s in danger. The medium falls back into her chair and tells him to leave.
Doyle and Stratton attempt to find the man the medium described. Doyle approaches a dirty man and asks him about the money he stole. The man runs and Stratton takes him down.
Doyle tells Houdini that they found the man through a medium. Houdini says he’s not their man.
Houdini says he examined the books and Sister Mathilda is embezzling from the laundry. Stratton says Mathilda was arrested for pickpocketing when she was 19.
Suddenly, the lights go out. Something flies above their heads and Mathilda is written in blood on the stage. Doyle tastes it and finds that it’s corn syrup. Houdini staged it to prove the supernatural can be faked.
Doyle asks Houdini why he can’t accept that there are things bigger than him. Houdini asks him why he can’t accept that this is all there is. Stratton stops their fight. A Scotland Yard officer tells them Sister Mathilda has been murdered.
Stratton finds writing on the window at the scene. It says, “All Things Come in Threes.” They ask Winnie why Mathilda was killed. She says Mathilda stood by while Lucy was locked outside. Winnie says Fabien, Mathilda and Grace murdered Lucy.
Stratton suggests compiling a list of girls who had to give up their babies who might hold a grudge. Doyle helps her with the list. He finds a name that sends him back to the convent.
Stratton comes to Houdini’s flat to discuss the case and finds him entertaining many famous people for his mother’s birthday. Stratton sees photos in Houdini’s office of false mediums. He says it’s up to him to stop them.
Stratton shows Houdini a map of secret passageways in the convent. There is a path from Lucy’s grave to Fabien’s office. Houdini asks why a ghost needs a passageway. He accuses her of being stupid and tells her to quit her job. She goes off, telling him women live in fear of ending up like Lucy. How dare he condescend her? He’s impressed.
Doyle calls Stratton and Houdini to the scene. He found a single daisy in a glass after Fabien’s murder. After Mathilda’s, there were two. Lucy’s baby was named Daisy. Houdini claims it’s about the money. Doyle says there was no robbery. Sister Fabien had the missing money.
The apparition appears in front of our investigators. Houdini is upset and says it wasn’t him.
Doyle goes back to the medium and asks what Lucy wants. The medium says she’s seeking peace. She comes through as Doyle’s wife again and talks about her death. Doyle then knows she’s a fake.
Doyle visits his wife in a hospital where she’s in a coma. Later, he dines with his children. His daughter asks if he was able to talk to their mother. He says he’ll keep trying. He gets an idea and leaves for the convent.
Houdini meets him and they speak to Sister Grace. Grace has flexible joints like Lucy. Doyle suggests Lucy was her daughter. Grace says watching Lucy die was her penance for her mortal sin, but she killed the others to bring Lucy peace.
Grace runs and Houdini and Doyle follow. She traps them in water beneath a passageway. Houdini tries to pick the lock with Doyle’s collar stay, but can’t manage.
Stratton lets them loose. She arrested Grace and left her in Fabien’s office. Doyle says Grace is the third victim.
Doyle tries to talk Grace out of cutting her own throat. It doesn’t work until Houdini says he feels Lucy’s forgiveness. The apparition appears and Grace drops the blade.
Houdini tells Doyle it was subsonic vibrations. They create the sensation of the chills and cause irregularities in peripheral vision. Houdini says they’re caused by the subway station put in around the time Lucy died. The train passes every 17 minutes. Doyle is impressed.
Stratton’s boss moves her upstairs by Houdini’s recommendation. He assumes she’s having an affair with Houdini and threatens to fire her when he can prove it.
Doyle goes to another medium. Houdini hears his piano playing, but nobody’s there.
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