John was never good at long car journeys. After about twenty minutes his head would begin to droop and he'd wake up an hour later with his face smacking against the window as the car went round a corner. He blamed his mother, who used to take him out for car rides when he wouldn't sleep as a baby.
This time he was determined not to fall asleep in a squad car that contained Detective Inspector LeStrade, Sgt Donovan, Dr Anderson and Sherlock. Because that would just be the most embarrassing thing that could ever happen to him. Only they got stuck in traffic coming back from Sevenoaks and John slowly began to drift off.
Anderson was in the front, safely away from Sherlock. Donovan was driving and John was sandwiched in the back between what seemed like several acres of Detective Inspector on one side, and a xylophone wearing an overcoat on the other. John had to go in the middle, because he was short, so Donovan could see out of the rear view mirror. So she said.
He felt his eyes beginning to close, three or four times and tried to snap himself back awake. But slowly the warmth in the car and the purr of the engine carried him off. Out for the count.
Sherlock noticed John Watson's head begin to nod. It bounced painfully every time the car hit a bump in the road. He was going to have a sore neck when he woke up. In the mirror Sherlock could see Anderson smirking at the unconscious John Watson, passed out like a little boy after an exciting day out. No doubt Anderson would enjoy telling everyone at the Yard about it.
Sherlock looked down thoughtfully for a moment and then put his arm around John's shoulders and pulled him close so his head was resting on Sherlock's chest. Anderson's eyes widened in the mirror. That would give him something else to talk about.
LeStrade turned his head to Sherlock a question about to tumble out into the quiet of the backseat.
"Shush. He's sleeping."