Coming up behind was another taxi—­an empty one, the driver leaning back in his seat puffing lazily at a pipe.  I stepped out into the road and signalled to him to pull up.

“Follow that taxi in front,” I said quickly.  “If you keep it in sight till it stops I’ll give you five shillings for yourself.”

All the languor disappeared from the driver’s face.  Hastily knocking out his pipe, he stuffed it into his pocket, and the next moment we were bowling up Victoria Street hard on the track of our quarry.

I sat back in the seat, filled with a pleasant exhilaration.  Of course it was just possible that I was making a fool of myself—­that the gentleman in front was as innocent of having spied on my movements as the Bishop of London.  Still if that were the case there could be no harm in following him, while if he were really one of McMurtrie’s friends a closer acquaintance with his methods of spending the evening seemed eminently desirable.

Half way along Whitehall my driver quickened his pace until we were only a few yards behind the other taxi.  I was just going to caution him not to get too near, when I realized that unless we hung on as close as possible we should probably lose it in the traffic at the corner of the Strand.  The soundness of this reasoning was apparent a moment later, when we only just succeeded in following it across the Square before a policeman’s hand peremptorily barred the way.

Past the Garrick Theatre, across Long Acre, and up Charing Cross Road the chase continued with unabated vigour.  At the Palace the other driver turned off sharp to the left, and running a little way along Old Compton Street came to a halt outside Parelli’s, the well-known restaurant.  As he began to slow down I picked up the speaking tube and instructed my man to go straight past on the other side of the street, an order which he promptly obeyed without changing his pace.  I didn’t make the mistake of looking round.  I just sat still in my seat until we had covered another thirty yards or so, and then gave the signal to stop.

The driver, who seemed to have entered thoroughly into the spirit of the affair, at once clambered out of his seat and came round as though to open the door.

“Gent’s standin’ on the pavement payin’ ’is fare, sir,” he observed in a hoarse whisper.  “Thought ye might like to know before ye gets out.”

“Thanks,” I said; “I’ll take the chance of lighting a cigarette.”

I was about to suit the action to the word, when with a sudden exclamation the man again interrupted me.

“There’s another gent just come up in a taxi, sir—­proper toff too from ’is looks.  ‘E’s shakin’ ’ands with our bloke.”

“Is he an old man?” I asked quickly—­“an old man with glasses?”

“’E don’t look very old, but ’e’s got a glass right enough—­leastways one o’ them bow-winder things in ’is eye.”  He paused.  “They’ve gone inside now, Guv’nor; they won’t spot ye if you want to ’op it.”