Okay, sorry this one's short. Please comment!!

 (Alice’s POV: )

Three Hours To Go; 221B

 Sherlock had moved to the side table in the kitchen and was looking into his microscope. Mrs. Hudson came in through the kitchen door with a tray containing a few mugs. I looked up from my book and smiled kindly at her. She smiled back and as she put the tray on the kitchen table, Sherlock looked up.

“Poison.” He said. I stood up and put the book back, excited.

“What you going on about?” Mrs. Hudson asked. Sherlock slammed his hands down on the side table.

“Clostridium botulinum!” He shouted. I grinned and went into the kitchen. Mrs. Hudson cringed and fled the kitchen. Sherlock looked round at John and I as he came in from the living room, leaving me to look into his microscope. “It’s one of the deadliest poisons on the planet!” He exclaimed. I looked up from the microscope and leaned on the side of the table, my arms folded and me smiling at John. He looked at us blankly. “Carl Powers!” Sherlock stressed.

“Oh, wait, are you saying he was murdered?” John asked, finally catching on. Sherlock stood up and walked over to where he had hung up the laces from the trainers.

“Remember the shoelaces?” I asked, moving next to Sherlock.

“Mmm.” John replied, a lot less eager than we were.

“The boy suffered from eczema. It’d be the easiest thing in the world to introduce the poison into his medication.” I said, allowing Sherlock to finish.

 “Two hours later he comes up to London, the poison takes effect, paralyses the muscles and he drowns.” Sherlock exclaimed happily.

“What – how-how come the autopsy didn’t pick that up?” John asked, spooked again that we were finishing each other’s sentences.

“It’s virtually undetectable. Nobody would have been looking for it.” I answered, taking my turn. Sherlock had walked around the table to where his computer notebook was lying. The page was open at the Forum of his own website, The Science of Deduction, and he began to type into the message box:

 “FOUND. Pair of trainers belonging to Carl Powers (1978-1989).” Sherlock straightened up and pointed at the laces.

 “But there were still tiny traces of it left inside the trainers from where he put the cream on his feet.” Sherlock said, bending down and continuing to type.

 “Botulinum toxin still present. Apply 221b Baker St.” He sent the message and straightened up again.

“That’s why they had to go.” I said.

“So how do we let the bomber know...?” John asked, looking at us each in turn.

“Get his attention...” Sherlock reasoned.

“Mmm-hmm.” John hummed.

“...stop the clock.” Sherlock said, looking at his watch.

“The killer kept the shoes all these years.” John said, amazed.

“Yes.” I said, Sherlock and I looking to John.

 “Meaning...?” Sherlock asked.

“He’s our bomber.” John realized. The pink iPhone rang on the side table. Sherlock hurried over to it and switched it on. In the car park, the woman sobbed in anguish as she read out the latest message from the pager.

“Well done, you. Come and get me.” She wept.

“Where are you? Tell us where you are.” Sherlock said, loudly and clearly.

Again, sorry it's short!