I've been reading a book in Japanese in order to learn new kanji, words, etc., but I've come across something I can't seem to translate. The sentence is as follows.
I'm familiar with all the words and grammar within the sentence, and, based on context clues, I think I have a rough understanding of what this sentence means. But I'm a bit uncertain of what なり切ってしまう actually means, as I don't think we're talking about the verb 'to cut'. It's my understanding that 切る has a good handful of other meanings, so I thought it must be one of those which I'm unfamiliar with.
And, to give a little bit of context in case that helps, this is from Edogawa Ranpo's novel「怪人二十面相」and the sentence above is describing the thief's ability to disguise himself.