An extra/other/wrong person, or wrong headcount

I read Annie Neugebauer's The Extra recently and I loved the premise.

Plot: Ten hikers go into the wilderness, but after a strange event, there are eleven people. The leader, Matt, knows everyone but can't explain the extra person, creating an atmosphere of paranoia and distrust.

Are there any other books like this? Not necessarily a doppelganger, but more like "there's something wrong here, someone is not who they say they are… Or there's an extra person, but I don't know who it is, and we need to figure it out before its too late."

It kind of reminds me of the Thing, which is a movie I absolutely love. I enjoy weird lit, thrillers/suspense and horror. I guess I'm mostly looking for something that invokes paranoia, dread, and tension. TIA!