Sherlock and John are captured by some criminal and tied up. Sherlock receives a call from Lestrade. The criminal holds a gun to his head and tell Sherlock to say everything is fine. Sherlock then repeats "Everything is fine, Greg" and Lestrade knows something is up because Sherlock never remembers his name
Sherlock Headcannons
By Helsing_Wick
All credit belongs Sir Arthur Conan Doyle and Moftiss More