Probably an easy one, I'm sure, but what episode is this, and WTF is that in the background? Has my brain blocked out an episode?
It's The Dauphin, and the monster was a shape shifter.
Season 2, The Dauphin. Enterprise plays taxi for a new head of state, Wesley does the teenager in love thing, falling for a cute nerd. I just watched this one but had to look up the title.