Star Trek: Enterprise (2001)

Season 1: Episode 9

Captain Archer and the crew discover a fully inhabited, civilized though less advanced Earth-like planet. Disguised to look like its inhabitants, they pay the planet an exploratory visit where they learn that a pernicious illness is afflicting the local population. As Archer seeks to help them find the malady's source, he finds himself in a close encounter with a comely female alien.