Additional\Sub-questions: What makes this story believable or unbelievable?
I think that it is very possible, however somewhat difficult, for a person to solve a crime the way Holmes did. It takes a little bit of practice, but it can be done. At first when Holmes tells us and John Watson the things he has gathered about Jabez Wilson’s character in a matter of minutes, we are confused and astonished at how he can know such things. But, when Holmes explains how he found out that Wilson “has done manual labour, takes snuff, is a Freemason, has been to China, and has been doing a lot of writing lately”, it becomes obvious how he knew those things. Had we been shown such clues as Holmes used to deduce those traits of Wilson’s, the more inquistive and thought-provoked of readers would have been able to figure it out without much of a problem. So, that is why I think it is perfectly believable that Holmes could have solved the crime of John Clay and the false red-headed league in the way that he did, especially considering the fact that he’s obviously had some practice before, in the form of his other adventures.