The Enterprise finds archaeologist Dr. Roger Korby, Christine Chapel's fiancé, who has been missing for five years, living underground on the deserted ice planet Exo III with a group of sophisticated androids, including Andrea and Ruk.

The female android, of course, is emotional. In this case, the artificial humans were not perfect copies, but Roger's "does this make such a difference?" is worthy of more thought. It's an issue dealth with in TNG in Data's story lines. The situation with the duplicate Kirk is resolved with a very convenient imperfection in the android.