In order to stablish 100% credibility of a source, you should keep in mind to:
Consider the author’s scholarly education: Within each field, there are a handful of scholarly thinkers considered the giants of the discipline. For example in literary theory, Jacques Lacan, Jacques Derrida, and Michel Foucalt are three towering figures whose work provides the bedrock of the discipline.
Avoid self-published material at all costs: If an author is unable to convince a publisher to house their ideas, it’s likely because their ideas carry little weight. Never cite an author who self-published their work.
You did not provide the excerpt but in the end Jekyll was not able to permanently resist. It was implied that he was actually Hyde deep inside and that Hyde is the one who will overtake and he won't be able to come out again. In the end he dies as Hyde and people find out what happened out of letters that he sent while he was sane.
