After two days of living with Molly, Irene had finally found the decency to wear Molly's clothes. Irene, of course, told Molly how dull her clothing was, but Molly ignored her. She didn't care what Irene, of all people, had to say about her sense of fashion. Irene was used to nice, fancy dresses, but Molly liked her simple trousers and shirts. She wasn't going to dress differently just because the dominatrix wants her to.

They both sat on the sofa watching telly. Molly had her arms around her legs and her chin rested on her knees. Irene sat with her legs crossed. Her elbow stood on her leg and her chin rest in the palm of her hand. They were both bored.

Suddenly, Irene's mobile rang. She took it out of her pocket and looked at the caller ID. Her smile told molly that either they had a case, or Sherlock was calling. The former, of course, was more likely.

Irene held the phone to her ear. "Hello, Detective Inspector…Where?...We'll be there in a few minutes…Goodbye." She hung up.

Molly put her feet back on the floor. "Greg?"

"Yes," Irene said. "361a Rosewood Street."

Molly and Irene stood up. Molly grabbed her coat and Irene put on Sherlock's, and they both headed outside and hailed a cab.

When they arrived at the crime scene, they approached the police tape, which provided a block on the street. Sergeant Sally Donovan stood there.

"If you'll excuse us, dear," Irene said to Sergeant Donovan. "We'd like to get through."

"No one can get through," Donovan informed her. "There's been a crime."

"We were invited by Inspector Detective Greg Lestrade." Molly said.

"Why?" Donovan asked."

"He wants us to investigate the body," Irene told her. "Why else?"

"Why would he invite you?" Donovan asked in a cold voice.

Irene took a step forward. "Because we were suggested."

Donovan took a step back. "By who?"

Irene took another step forward. "Sherlock Holmes."

Donovan crossed her arms. "I still can't let you in."

"Would you like me to call Greg?" Irene asked.

Donovan finally rolled her eyes and lifted the tape.

Irene stepped under. "Thank you, dear."

"Thanks." Molly said as she followed Irene.

They walked up to the flat where the crime took place. Phillip Anderson was waiting at the door. As they approached the door, he stopped them.

"You can't go there." He said.

"Oh please," Irene said, pushing Anderson out of the way. "We've already been through this with Sergeant Donovan." Irene pushed open the door and walked inside.

"Sorry." Molly said to Anderson as she followed Irene.

There were people inside. They all were dressed in light blue coveralls, shoe covers, and gloves. Lestrade was waiting inside.

"Molly?" Lestrade said as Irene and Molly approached him.

"Greg." Molly greeted.

"What are you doing here?" Lestrade asked.

"She's with me." Irene told him.

"And you are…?" Lestrade asked.

"Irene Adler." She said.

"Oh, yeah," Lestrade extended his hand in front of him, but took it back when Irene didn't shake it. "Sherlock told me about you. The body is through there, but you'll need to put on coveralls as well.

Molly put on the coveralls, but Irene refused. All she put on was the gloves.

When they entered the next room, the body lay in the centre of the floor. The room was clear of furniture, and the wallpaper was [peeling. There wasn't any light, all light bulbs were missing from where they should have been.

"I'd say she's in her twenties," Molly said as she crouched in front of the body.

The woman lay on her stomach. He head was turned to the left and it was streaked with blood. Irene got on her knees next to Molly. And touched the dead woman's cheek with her hand.

"No cuts where the blood is," Irene said. "There is a wound on the back of her head. She was killed by a deathblow to the back of the head with a blunt instrument."

Molly moved to the woman's legs. "Her legs are broken," Molly felt the woman's legs through the dark jeans she wore, which were wet with blood. "Both of them. I'll guess that it happened before she was killed."

Irene felt her arms, which were wounded as well. "Her arms are broken too. Most likely before her death."

"She may have fallen…" Molly trailed off.

"But the killer could have done it as well." Irene finished. She turned to Lestrade, who was standing in the doorway. "Was anything found with her? A purse, handbag, anything; an umbrella, even?"

"No," Lestrade said. "Nothing. She didn't even have a phone. The room was empty, along with her pockets."

"Go get me a torch," Irene told him. "Get Molly one too."

Lestrade left and came back with two torches. He handed one to Irene and the other to Molly. Irene stood up and shined to torch on the wall. Molly did too.

"What are we looking for?" Molly asked.

"Anything," Irene said as she walked round the room. "There must be something. Every killer leaves something behind."

"Because…" Molly began.

"It wouldn't be any fun if thy didn't." Irene finished.

"What would they have left?" Lestrade asked.

Irene moved to the other side of the room. "Any dent in the wall," Irene said. "Any stain, anything." She turned to Lestrade. "Have you lot even bothered peeling back this wallpaper?"

Lestrade said nothing.

A few minutes later, Molly stopped walking.

"Irene," Molly said. "Come look at this."

"What is it?" Irene asked as she walked over to Molly.

Molly rubbed the palm of her hand over the wall. "There is an outline in the wall. Like something is carved into it."

"Rectangular." Irene said, placing her hand on the spot being investigated.

"Something is hidden under the wallpaper," Molly said. "Could be a trap door. Maybe there is a hidden compartment."

"Maybe it holds a clue." Irene said.

"Yeah," Molly said. "Maybe."

"Lestrade," Irene said. "Get someone who can get to whatever this is."

Awhile later, they had found a compartment in the wall. There was a piece of paper in it. Molly reached in and picked it up. It was blank. She turned it over in her hand and stared down at scribbled words in a foreign language.

"L'appel du vide?" Molly said.

"What?" Lestrade asked, walking over to her.

"L'appel du vide," Molly repeated. "That's what this says."

Irene took the paper from Molly and stared at it.

"What does it mean?" Lestrade asked.

"L'appel du vide," Irene said. "It's French."

"Alright then," Lestrade said. "What does it mean?"

"Call of the void." Irene said.

"You speak French?" Molly asked. Irene ignored her.

"What exactly does that mean?" Lestrade asked Irene.

"You know how when you are on top of a high building, or a cliff, and you just have the urge to throw yourself off? Fall to your death, even though you have no desire to die, well usually you don't. Well, that's l'appel du vide. Call of the void."

"And that's a clue?" Lestrade said.

"That's the killer's message to us." Molly told him.

"Exactly." Irene said.

"So, what?" Molly asked. "This woman jumped off something, and survived. The killer, whoever they are, killed her?"

"More like euthanized her." Irene said.

Irene tossed her torch to Lestrade, and Molly gave hers back. They both headed towards the door, Molly stripping off her coveralls.

"I think we're done here, Detective Inspector," Irene said. "We'll investigate the corpse back at Bart's."

Irene and Molly left the scene before Lestrade could say anything to them.