how the hell did the kid not realize not to drop the bomb? The friggin' alien was the one pushing hardest of all to drop the bomb! So many chances to fail and yet it was the alien who pushed them onwards. At the end after the weapon's officer gives up he persists in finding a way to arm the bomb. Once the weapon is armed the weapon's office even says that "something is wrong" and then is killed, with the alien revealing herself.
The kid was already suspicious that the aliens knew of the attack. Why didn't he put two and two together? The portrayed him as a smart kid, seeming well informed on a lot of subjects. The point can be made that he was dieing of radiation sickness and so probably not thinking super clearly but still, it seems a bit of a stretch.
Outside of that I really like the episode, one of the better ones in the series. I would have given it a 5 if not for the implausibility of the ending.