The threat involved in the 10-episode season involved a substance called zero matter, which was accidentally unleashed during the test of a nuclear bomb. An actress/scientist (who was a character inspired by Hedy Lamar, who was an actress and also an inventor) becomes infected with the zero matter and attempts to become all-powerful. I will not spoil the storyline for those who have not seen it, but like the first season, it packed a lot into the small number of episodes. Most of the main season 1 characters make at least an appearance in season 2. Howard Stark appears at the beginning of the season and again at the end, similar to how he was used in season 1, which works well for the show. James D'Arcy, Chad Michael Murray, and Enver Gjokaj return from the first season to star as Edwin Jarvis, Jack Thompson, and Daniel Sousa, respectively. Bridget Regan (Dottie Underwood) and Lyndsy Fonseca (Angie Martinelli) also returned in more limited roles.
The show was again well written and acted. It tied some real science into a totally made-up scientific storyline, which was nice to see, and also touched on social issues like racism and sexism. The show was unfortunately canceled after it was aired, so it ends on a pretty big cliffhanger, which will not be resolved unless it miraculously gets picked up now that Atwell's new show Conviction was also canceled. While anyone who has seen Captain America Civil War and the prior season of Agents of S.H.E.I.L.D. knows the fate of Carter herself, the cliffhanger set up what would have been a big story arc going into a third season.