He tried everybody except Plank.

He had scarcely the impudence to go to Plank just yet; but when, completing the vicious circle, he found his borrowing capacity exhausted, and himself once more face to face with the only hope, Plank, he sat down to consider seriously the possibility of the matter.
Of course Plank owed him more than he could ever pay--the ungrateful parvenu!--but what Plank had thought of that cheque transaction he had never been able to discover.
Somehow or other he must put Plank under fresh obligations; and that might have been possible had not Leila invaded the ground, leaving nothing, now that Plank was secure in club life.
Of course the first thing that presented itself to Mortimer's consideration was the engineering of Plank's matrimonial ambitions.
Clearly the man had not changed.

He was always at Sylvia's heels; he was seen with her in public; he went to the Belwether house a great deal.

No possible doubt but that he was as infatuated as ever.

And Quarrier was going to marry her next November--that is, if he, Mortimer, chose to keep silent about a certain midnight episode at Shotover.
It was his inclination, except in theory, to keep silent, partly because of his native inertia and unwillingness to go to the physical and intellectual exertion of being a rascal, partly because he didn't really want to be a rascal of that sort.
Like a man with premonitions of toothache, who walks down to the dentist's just to see what the number of the house looks like, and then walks around the block to think it over, so Mortimer, suffering from lack of money, walked round and round the central idea, unable to bring himself to the point.
Several times he called up Quarrier on the 'phone and made appointments to lunch with him; but these meetings never resulted in anything except luncheons which Mortimer paid for, and matters were becoming desperate.
So one day, after having lunched too freely, he sat down and wrote Plank the following note: My Dear Beverly: You will remember that I once promised you my aid in securing what, to you, is the dearest object of your existence.