I had had so many reasons to believe in my friend’s subtle powers of reasoning and extraordinary energy in action that I felt that he must have some solid grounds for the assured and easy demeanour with which he treated the singular mystery which he had been called upon to fathom.
Sherlock Holmes was a man, however, who, when he had an unsolved problem upon his mind, would go for days, and even for a week, without rest, turning it over, rearranging his facts, looking at it from every point of view until he had either fathomed it or convinced himself that his data were insufficient.
There are no more uses of "fathom" in the book.
Show samples from other sources
When I look at the shift my life has made in the past eight months, I can’t fathom what my life will be eight months from now.
Colleen Hoover -- Slammed
He couldn’t fathom why WICKED felt it was so important to keep their minds clean of memory.