When a meteor impacts not far from Terra Nova the resulting EMP shockwave fries all the electronics in the colony: Communication is down, those fancy shockwave guns stop working (I guess there's something to be said for gunpowder after all), the advanced medical equipment goes offline and their vehicles stop working (I guess there's something to be said for gasoline engines after all).
An interesting side note is that we learn that the perimeter is also down so there IS some sort of (electronic) defense that usually keeps large predators away from the colony.
The power outage leaves the members of the Shannon family all with their own little adventures:
Maddy is on a romantic picnic with her soldier boyfriend Reynolds when they realize that their communication and their car stopped working. So they need to head back to camp by foot but are unable to do it before nightfall, which is when most of the predators come out, e.g. some raptors...
Elizabeth has her hands full with a lot of wounded after the sonic shockwave of the meteor impact has reached Terra Nova leaving Skye to pull out a large tapeworm out of a friend of hers.
Jim and Zoe are stuck in an interesting computer database room whích only features a manual release for the door on the outside (so people breaking in don't need to bother using a pin code).
Mira and the sixers also try to take advantage of the situation and manage to finally steal the strange unknown object the Terra Novans had in their possesion. To achieve that they scared something that looked like a spinosaurus with fire towards Terra Nova where - luckily Taylor had anticipated that a wooden fence might not be a good protection against large predators when the perimeter defense and the weapons don't work...
The episode did have it's flaws and logic holes large enough to fit the mentioned spinosaurus right through it (how does one repair a fried computer chip to get a computer chip fabrication device running if he does not have any electronic means and obviously no other way of chip fabrication?). Leaving these flaws aside "Nightfall" was still far from being perfect. But it was a huge leap in the right direction. It did build up some suspense, it did have action, it did have dinosaurs, it did do the setting justice and it seasoned the mixture with an appropriate amount of humor. I really enjoyed the episode and I believe "Nightfall" to be the very best episode of Terra Nova this far.
With some revelations about the bad guys and someone they work for in the end Terra Nova finally seems to be headed into the right direction. Let's hope they continue and we can see Terra Nova become the show we all expected after the first trailers and a show worthy of the somewhat unique setting.