Agents of S.H.I.E.L.D., ABC
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Caution: So many spoilers!
I've decided to categorize this show as "action/adventure," though it has elements of various other categories, such as "mysterious," "paranormal," "science fiction," "superheroes," and probably other stuff. It's officially part of the "Marvel Cinematic Universe," but unlike the movies in that franchise, there are no superheroes in the main cast of the show. Of course we do see superheroes and supervillains from time to time, but they're not the main focus of the series. But while I'm on the subject of the movies, I should mention that the series premiere is set after Iron Man 3- the first movie in "Phase Two" of the cinematic universe- but before the next movie in the franchise. Incidentally, I didn't get a chance to see Iron Man 3 in theaters, so I had to order the DVD, which came out the same day this show premiered. I'd say it was worth paying a few bucks extra to make sure it got here in time to watch the movie before the series premiere, though it's not really necessary. During the course of the first season, two more "phase two" movies would come out- Thor: The Dark World and Captain America: The Winter Soldier- though I had to wait for the DVDs, which was a bit irritating, but it didn't greatly affect my appreciation of the show. Anyway, there will be numerous allusions to people and events from all the movies, throughout the series. But basically, it's about a clandestine government agency- Strategic Homeland Intervention, Enforcement and Logistics Division- which is made up of essentially ordinary human beings who must deal with out-of-the-ordinary threats. (Well, the agents may not be "ordinary," since they are highly skilled in various ways; I just mean none of them are metahumans. Apparently.) Anyway, it's a fairly clever and amusing and fun and interesting series. Oh, and you should probably check out the M.A.O.S. Declassified web show, because it's pretty fun.
My knowledge of the SHIELD organization of the comics is practically nonexistant, though I've seen it in other incarnations in various shows and movies, aside from this particular cinematic franchise. But it seems that most of the show's main characters are new creations, though one character, Phil Coulson, was seen throughout the movies. And in the pilot, we see Maria Hill, who was in The Avengers (as well as other incarnations with which I'm less, if at all, familiar). (Both Coulson and Hill are played by the same actors in the show as in the movies, and from time to time other characters from the movies appear on the show, also played by the same actors.) I should say, you really should not start watching this series unless you've seen all the movies in Phase One of the Cinematic Universe; and if you have, then you know Coulson died in "The Avengers." But he's back to life in this series. The series premiere explains that away... but a bit later in the episode, it is implied that the explanation is a lie, and that even Coulson himself doesn't know the truth. The truth is eventually revealed, but it's a major running mystery throughout the first season. Anyway, Coulson assembles a new task force to deal with particularly strange cases, which rather forces me to ask... Uh, isn't that what SHIELD is for in the first place? But whatever. Anyway, his team mainly operates from a highly modified Boeing C-17 Globemaster III, called "the Bus." (We'll also sometimes see smaller planes called Quinjets.)
One of the agents he recruits for his team is Melinda May (Ming-Na Wen, the only actor in the main cast with whom I'm greatly familiar from other things). Of course, the show's creators/exec-producers include Joss and Jed Whedon (and Jed's wife, Maurissa Tancharoen), so we can expect to see actors who've been in other Whedon shows or movies show up, from time to time. (In the pilot we saw J. August Richards, from Angel, and Ron Glass, from Firefly. We do see Glass's character, Dr. Streiten, in a later episode, briefly. And Richards's character, Mike Peterson, appears in several later episodes.) Anyway, Agent May apparently used to be a field agent, though for awhile now she's had a desk job, and is reluctant to return to the field. But she's a totally badass fighter, and also pilots the Bus. (She has a nickname within SHIELD, "The Cavalry," which she hates, so her teammates avoid calling her that.) Another badass agent Coulson taps for his team is Grant Ward, a black ops specialist who prefers to work alone. And there is a duo of scientists, Leo Fitz and Jemma Simmons, who work so closely together that people call them "Fitz-Simmons." (Fitz is an engineer and Simmons is a biologist, but they're both brilliant and they often work on the same stuff, regardless of their individual specialties.) Also in the first episode, there's a hacker named Skye, who's part of a group called the Rising Tide, which wants to expose the clandestine activities of SHIELD, among other things. So, she doesn't trust the organization, but ends up being recruited by Coulson, as well. Eventually, Ward begins training Skye, as her S.O. (supervising officer), so she can become a badass, as well.
Well, I don't want to get into all the different cases Coulson's team investigates. But there are various plot threads running throughout the season, and while some cases may indeed be isolated events, others that seem isolated may later turn out to play into the overall story arc. One recurring threat that SHIELD faces is a secret project called Centipede, which is run by a woman named Raina. But actually, Centipede is just one part of an even larger threat. Raina, and various other enemies SHIELD faces throughout the season, works for someone called "the Clairvoyant," who supposedly has psychic abilities that let him know pretty much everything that SHIELD wants to keep secret... the one exception being the truth about how Coulson was brought back to life. So that's something that both Coulson and the Clairvoyant want to learn about. Another plot thread involves Mike Peterson, a man with super powers (which had been given to him by Centipede) whom SHIELD tries to help, but eventually he gets transformed into a cyborg called Deathlok, controlled by the Clairvoyant. There are various recurring characters I should probably mention, like a wealthy businessman named Ian Quinn, who has ties to the Clairvoyant and is therefore an enemy of SHIELD. And Victoria Hand, who is in charge of the main SHIELD base, the Hub. And John Garrett (Bill Paxton), a SHIELD agent and old friend of Coulson's, as well as Agent Ward's former supervising officer. Garrett is currently S.O. to an agent named Antoine Triplett. And um... eventually the Clairvoyant's identity is revealed, but I don't want to spoil that. I will spoil the fact that he's a member of Hydra, an evil organization that had supposedly been eliminated during World War II (in Captain America: The First Avenger). But now Hydra is back, and they cause a great deal of trouble for SHIELD. (This is the central plot point of "The Winter Soldier," which came out 3/4 of the way through this season, but which I didn't see until halfway through season two.) After it turns out there are lots of Hydra sleeper agents in SHIELD, SHIELD itself comes to be considered a terrorist organization, so Coulson's team spends the remainder of the season trying to thwart the Clairvoyant's plans while also evading the authorities. The person in charge of finding and shutting down SHIELD bases is Air Force Colonel Glenn Talbot (Adrian Pasdar). Coulson's team moves to a secret base in Ontario called Providence, where they meet its caretaker, a SHIELD agent named Eric Koenig (Patton Oswalt). But Talbot eventually takes control of Providence, so the team has to relocate yet again. In the season finale, they arrive at a base called The Playground, where Eric's identical brothers, Billy and Sam Koenig, work. (Actually, I think Sam isn't seen until season two.) Anyway, Coulson's team finally defeats the Clairvoyant, but... I'll wait until next season to spoil some other things.