John heard the bell but did not move to answer it. No one at the door could be more important than his lap full of Sherlock. The bell rang again. Then two more times. Then Mrs. Hudson screamed.

Suddenly the doorbell was important. John settled Sherlock gently on the couch and stood.

Drawing his gun, he made his way silently to the door, which he cracked open to see the intruder.
There stood Lestrade, trying to calm a shaking Mrs. Hudson.
Ma'am, you need to sit down. Ma'am!"
John was angry, to be honest. And when John gets angry, it's not so farfetched that he may pull a gun on his brother in laws runaway husband.

"Mrs. Hudson," John said stiffly. "Why don't you go have a cup of tea. I need a word with our visitor."

Mrs. Hudson looked up at John, the guest, and John again. "Shout if you need me," she said, but she gave a look of disgust at Lestrade, that clearly showed her desire to 'help' the situation. Then she left.

"So. You come here. Now. Why?" The guest opened his mouth, but John interrupted from his place at the top of the stairs. "If I'm not satisfied with your explanation, I will blow a fucking hole through your skull. And I will get away with it. So this better be pretty damn good."
"I'm not the Detective Inspector," the guest said.
"I don't want to play any bloody word games, Lestrade. Why are you here?"
"I'm not Lestrade. Or at least I don't think I am. My name's Ryan Stone. Born in London. Moved to New York at 17. Learned to be a mechanic. Married Susan Burnstein. I have a very simple life."
"You expect me to believe that shit?" John asked, incredulous.
"I- um- here, I'll prove it!" The man said, pulling out his mobile. "I'll call Susan, she's my wife." He dialed and put the call on speaker.
"I told you that if you go to London, I'm not interested in phone calls from you," a female voice said on the line.
"Um, yeah. Sorry. I was just wondering when our wedding was again. I'm at a pub with some colleagues and they wanted to know. I slipped to the bathroom," Ryan rambled.
"You forgot again?! How many times Ryan? It'll be nineteen years this November. Now don't call me again till you're in America. I don't care if you forget your own name. Don't call."
The line went dead.

"But that's not possible," John practically whispered.