Sherlock thinks about ignoring him too, just waiting till John went away, but the promise of something he wanted was right there and even though he was sure it would blow up in his face... he'll stand, move to the door and the sound of it unlocking greets John first, before Sherlock creaks it open, just enough to peek his head through.

"Did Mycroft put you up to this?" He squints at him a little, watching him, observing how he reacts. Any little tell that would give him away, twitch of an eye, nervous rapping of fingers, him glancing to the side in a lie... something anything. He wanted to catch it and decide for himself if this was really worth the trouble. Because it was just obvious there would be trouble, he was Sherlock Holmes after all.