The Crimson Cryptogram by Fergus Hume

It was in a state of subdued excitement that Ellis left the rooms of Zirknitz. He now seemed to be nearer solving the mystery than he had ever been before. There was no doubt that Moxton had been murdered in order to obtain the forged bill; but Ellis was uncertain in his own mind whether Busham had actually struck the blow. A silk hat and a fur-lined coat was not a distinctive dress on a cold evening for any man -- a dozen might wear it. Still, the coincidence of dress was striking. Busham might be the criminal, after all, and Ellis drove directly to Esher Lane for the purpose of satisfying himself on this point.

What the doctor particularly wished to know was who had forged the elder Moxton's name? If Busham had done so he would scarcely have given the bill to Edgar, who had no great love for him. To hand him over an incriminating document and then murder him to get it back again would have been the height of folly. If, therefore, Busham was innocent of the forgery, he would scarcely risk his life in endeavouring to recover the bill. Thus, if anyone had a reason to desire the death of Edgar, it must have been the forger himself. Having committed one crime he certainly would not hesitate to commit a second, if only to conceal the first. This theory was excellent, and Ellis wished to prove its truth. To do so, it was necessary that he should learn the name of the man who had forged the bill. Busham had given the document to Edgar Moxton, as was asserted by Zirknitz, therefore Busham could inform him of what he wished to know. But would he do so?