Alien fly

A species of "alien flies" attempted a subtle invasion of Earth in the early 21st century, possessing the ability to assume human form. They were thwarted by Trinity Wells with support from Jack Harkness. (AUDIO: Driving Miss Wells)

Behind the scenes

 * The revelation of the human-form aliens, whose speech changes "s" sounds to a buzzing "z", is identical to that of the wasp-shaped Vespiform in TV: The Unicorn and the Wasp.