With shining eyes Sherlock watched the chemical reaction, separating the liquid rubber from the tainted drug. As soon as it settled he dipped the litmus paper into the brackish looking liquid sitting at the top of the test tube.

It didn't take long for it to turn yellowy orange, the chemical taint making it far more acidic than the purer control samples.

Quickly noting his results, he turned off his burners and made a half-hearted attempt at making sure the lab was safe, then grabbing his notebooks he rushed upstairs.

Looking around the living room he remembered John saying he was going out for a while, although a glance at the clock showed that that had been nearly four hours ago. With a frown he picked up his phone.

There were two missed calls, both from his brother. He opened the voicemails and listened.

"Sherlock, when you pick this up please ring me. It's urgent, so please don't ignore it for the sake of point scoring. I've also left messages for John."

He pressed recall.

"Sherlock, thank goodness." Mycroft sounded relieved. "Are you alright?"

"Of course I am, I've finally cracked the chemical binding. Why, what's going on?"

"You haven't seen the news? Every mainline station in London has been bombed."

There was an ominous silence, then

"John hasn't come back."

A/N: Thanks to MrsPencil and Jack63kids for their help on this chapter :)