Knowing that Mark was unlikely to be free until four o'clock, Colin decided that he might as well accept the invitation. He had never been inside Scotland Yard, and the prospect rather appealed to him.
"What shall I do with the car?" he asked. "Leave it here?"
"Better bring it into the yard," said the Inspector. "No one will try to pinch it then—not unless he's a bit of an optimist."
Getting into his seat, Colin started forward alongside his companion, and turned in through the big iron gates which guard the headquarters of the London Police Force.
There were several other cars standing against the wall, and, leaving his own in company with them, he followed the Inspector through a low doorway and up a long flight of stone stairs.
They emerged into a broad corridor with doors on either side.
"Here we are!" announced his guide, halting in front of the second. "I don't know who's on duty to-day, but we're sure to find somebody about."
He led the way into a large, business-like apartment, the principal furniture of which consisted of a couple of roll-top desks. At one of them was seated an alert-looking man in a well-cut blue suit, who glanced up sharply at their entrance.
"Hullo, Pat!" said the Inspector. "I've got someone here I want to introduce you to. This is Doctor Gray of St. Christopher's Hospital."
The other laid down his pen, and, rising from his chair, shook Colin's hand.