Five years.
Five years of finding a balance between police procedure and infuriating genius. Five years of knocking a brilliant brat back onto the straight and narrow when he needs it, and learning just when to look the other way. Five bloody years of coming when he's called and tolerating quirks and lectures for the sake of his profession, and then up shows a complete stranger, an amateur, with a come-and-go limp and a hero complex, and five hours later Lestrade knows that he has lost the title of "closest thing to a best friend Sherlock Holmes has ever had."