Alien invasion is such an old cliche, that it’s hard to imagine there’s something new you can do with this theme. Threshold was a short-lived, one season series that had a more or less fresh take on it. Instead of an Independence Day-like alien invasion the aliens send a probe that transforms humans using a sound signal, making them stronger and more resilient in the process, but also much more violent. The transformation also implants alien memories and urges into their mind, in effect destroying the original personality and supplanting it with a mindset slaved to follow the alien imperatives, which means infecting more humans.
One of the main concepts of the show was a contingency plan to handle an alien invasion, made by a Dr. Molly Caffrey. She was one of the lead characters of the show, her job to implement her own contingency plan. While I thought this idea was a bit far fetched, a plan made years ago could be usable instead of accessing an actual situation and making a strategy by reacting to real-time events. Since the plan is never explicitly written out, the writers of the show could actually change elements at will. Even then, it’s shown later in the series that some events were not foreseen in the plan (called Threshold, to explain the name of the show) and had to be dealt without the plan as a safety net.
While the theme and setting is pure science fiction, the structuring of the episodes and the interactions of the characters made this more drama than mere action-adventure, with some nice acting from all characters. Overall, while an old theme, it’s realization was pure gold and actually very much fun to watch. Especially since toward the end of the show it didn’t looked like the infection could be easily contained. There were plans to make two more season, each showing a new level of the contingency plan for an ever more escalating situation, named Foothold and Stranglehold. There were also hints that something more than just mere invasion was behind the alien motives. I really would have liked to see the show complete its run.