He got wrong, somehow, and he forged the Duke's name to a cheque.

Now, then, considering who Glassdale is, and that he was certainly a fellow-convict of Brake's, and that I myself saw him here in Wrychester on the day of Brake's death--what's the conclusion to be drawn?
That Brake wanted to see the Duke on some business of Glassdale's! Without a doubt! It may have been that he and Glassdale wanted to visit the Duke, together." Bryce silently considered this suggestion for awhile.
"You said, just now, that Glassdale could be traced ?" he remarked at last.
"Traced--yes," replied Harker.

"So long as he's in England." "Why not set about it ?" suggested Bryce.
"Not yet," said Harker.

"There's things to do before that.

And the first thing is--let's get to know what the mystery of that scrap of paper is.
You say you've found Richard Jenkins's tomb?
Very well--then the thing to do is to find out if anything is hidden there.