Quote Originally Posted by Dogboy182
In english, if you said "the third person, it sounds like, there is someone else in the house that you don't know, and they might be trying to kill you or something.
Yes, the same in Russian. I'd also prefer saying "кто-то другой" or "кто-то ещё" to "кто-то третий" in that kind of situation and "кто-то третий" really implies more suspicion here.