He called: “Jolly!”

Jolly was in the room in a trice.

“Have you ever seen this girl before?” asked Rollison, making way for his man. “The one in the olive green trouser-suit.”

Jolly, who had to go closer to the window in order to see out, said simply : “No, sir.”

“But we’ll recognise her if we see her again, won’t we?” Rollison mused.

“Would you like me to follow you in the Austin, sir?” asked Jolly, no doubt hopefully.

“So that you can follow her if she follows me,” inferred Rollison. “No, I don’t think so. I’d rather you were here in case some quick action on the home front is called for. But watch to see if she follows me out of the street.”

“I certainly will,” promised Jolly.

Rollison went towards the front door.

The unique quality of the apartment was that it had a lounge hall with a passage leading towards the domestic quarters and the bedrooms, and a door into the big study-cum-living room with its dining alcove. Along a continuation of this was a passage also leading to bed-rooms and the domestic quarters. Two people could play hide-and-seek for a long time in the flat. Rollison, encouraged and at times inspired by Jolly, had made some refinements. Both doors — the front one and the one leading to the fire escape from the kitchen — could be locked and made virtually impregnable. So could all the windows. Moreover, above the lintel of the front door was an ingenious contraption based on the principle of the periscope. By glancing up from inside, one could see the landing and the staircase beyond; and so be fore-warned if anyone lurked there.