"Yes," she answered, looking at him. She didn't even look like anything more than a dog groomer.

"You are the sister of our victim's late wife, are you not?" Sherlock continued, watching her expressions.

"That's right," Kelly said, swallowing. "He is--was--my brother." She blinked a few times.

"Brother-in-law," Sherlock said absently. "Your sister-- It was a car crash, correct? And not all that long ago, either, it was very recent."

Kelly nodded. "That's right. I was the maid of honor at the wedding." She sniffed. "My whole family was very fond of him, we all thought my sister had picked a good man. And then she died, and he was so broken up over it..."

"Was that why you decided to comfort him the way you did?" Sherlock asked with mild curiosity.

"I-I don't understand," Kelly said, though she didn't meet his eyes, instead fumbling with a button on her coat.

"Don't you?" Sherlock asked. "Making plans with him, boarding your dog... You certainly didn't sound broken up on the phone. On the contrary, it sounded very much like plans for a weekend away together."

"He just needed to get out of the city for a few days," Kelly said. "That's all. There's no harm in that."

"A weekend alone with his late wife's sister, indeed," Sherlock said. "I'm sure you had all sorts of things planned for just the two of you."

"I was going with as moral support," she said, looking at him. "He was lonely after my sister died, and he needed company, poor thing didn't have many other people in his life."

"Clearly enough people in his life to be murdered by one," Sherlock pointed out.

Kelly shrugged. "I dunno," she said. "I didn't do it, I was still planning on us going away for the weekend." She sniffed again.

"Strange, then, that you would have already kenneled your dog three days before the start of the weekend?" Sherlock suggested. "Perhaps there are more factors at play. Let's review, shall we? Your sister's husband, with whom you had planned at least one date -- don't give me that look, it was very clearly supposed to be a date -- and it likely wasn't the first. Which leads me to believe that you might have even been seeing him behind your sister's back, with how efficiently you set up your plans this time. The accident was, while tragic, also a stroke of luck, because now the field was clear for you to move in. Do correct me if I'm wrong, but I doubt I am."

Kelly pouted a bit but stayed silent, not contradicting him.

"Except you just proved a quite excellent reason not to kill him," Elena murmured to him, amused.

"I'm not finished yet," Sherlock said. He studied Kelly for a moment. "Your way was clear, except for one thing. The victim himself. Your sister probably found out about the affair, likely the day of the accident, and the victim blamed himself for it. Blamed himself and then broke it off with you, I'm assuming, and that just wouldn't do, would it? And they do say hell hath no fury like a woman scored..."

"What?" Kelly blinked. "No. I didn't start anything with him until after my sister died, I was living out of the country until then, I moved back home for the funeral and to help my parents. I was working in the United States, in New York."

Elena grumbled something uncomplimentary about New York.

"You didn't protest when I mentioned the affair before," Sherlock pointed out. "I even pointed out you were seeing him before the accident, which you didn't deny." He smirked, having caught her in the lie. "Now, tell me, why did you kill him?"

"I didn't. I was at work when he was killed," Kelly said. "Ask my coworkers, there were a few of us there, we were chatting about the holidays and working."

"You were at work when he died, not when he was killed," Sherlock said. "Do try not to lie to me, it doesn't work."

Elena slipped from the room to go check on a few things, because something wasn't adding up here.

"I didn't kill him," Kelly said, frowning at Sherlock. "Why would I?"

"Why indeed?" Sherlock replied. "The logical assumption is that when you realized he would never love you the way he loved your sister, you decided nobody would have him."

"No," Kelly said. "I'm not ready to settle down yet, I don't want to. This was just a... a thing. Just for a while. I don't want to get married or be stuck with one person for the rest of my life."

"Of course not," Sherlock said, studying her carefully. "Young, vivacious, likely a string of broken hearts in your wake. What made this man so different?"

"Nothing. We were going to go away for a weekend, we had plans to get together fairly frequently."

"Sherlock," Elena murmured as she moved back into the room with some records. "She was living in the US until the sister died." She handed over the files.