[...Oh, shit. Sherlock stalls, presses his lips together tight and tries to shake his head, but no. It all starts pouring out at his usual rapid clip.]

I'm sending a text to Lestrade. Apparently the purpose of the gas is to make people compliant to any orders or requests given to them; not only compliant but it creates the compulsive necessity to carry them out. That's why I agreed so quickly to everything everybody was telling me to do for the last half hour, although they were reasonable enough requests, which is why it took me only until now to realize it. Culprit must have had some pretty sick and twisted stuff in mind, or perhaps he only wanted agreeable hostages, either way the gas would have allowed him to have complete and utter control over their actions.

[But okay. He's going to try to play this cool. Perhaps John won't take advantage of it. Much.]