Partly set during the day that SHIELD fell (i.e. during the events of Captain America: The Winter Soldier) and partly set in the present day, "One Door Closes" has Bobbi infiltrating Coulson's SHIELD in order to steal Fury's toolbox while we learn through flashback how and why the "real SHIELD" came to be. At the same time, Skye meets Gordon, the teleporting Inhuman, who offers her a chance to join a colony of other Inhumans.
What "One Door Closes" excels at (and what I imagine the main purpose of the episode is) is creating a good reason for 'real SHIELD' to exist, one that makes sense and allows the audience to further understand why they are doing what they are doing. Told in flashback, we see Bobbi and Mac on board the Helicarrier commanded by Agent Gonzales as they try to retake the ship from Hydra during the events of Captain America: The Winter Soldier. Despite the washed out colour of these scenes giving everything a B-movie vibe, the story being told is pretty good, the action is well done and the return of Lucy Lawless as Isabelle Hartley is a nice touch that helps quantify the reason for Gonzales' unease with Coulson being the director of SHIELD.
Between these segments and the infiltration of SHIELD by 'real SHIELD', "One Door Closes" is potentially the most action packed episode of the series to date, a particular highlight being the confrontation between Bobbi and May. The choreography isn't as good as the May versus May fight from "I Will Face My Enemy", but it's still fun to see these two highly dangerous agents go at each other. Additionally, there is a great sense of tension throughout the entire episode thanks to the whole spy versus spy thing - it's hard to tell who knows what, and this is played off well when Simmons runs into Bobbi late in the episode.
Despite the busy nature of the rest of the episode, Skye's side story is developed quickly too. I won't go into too much detail about what happens or how it overlaps with the SHIELD versus 'real SHIELD' storyline, but it's another example of Agents of SHIELD having a clear sense of direction now, and Skye's story over the next few episodes should be interesting to say the least - there is a lot of potential for some really cool new characters to be introduced here, and once again I'm led to believe that Agents of SHIELD could well be at the forefront of moving the Marvel Cinematic Universe forwards.
In an episode that could have been a giant mess of scenes thanks to it's non-chronological nature, "One Door Closes" is instead one of the most entertaining and action packed episodes of the series so far, and continues to prove that Agents of SHIELD isn't afraid of moving forward quickly and concisely any more. I'm really looking forward to seeing how all these groups will eventually be bought together, and with the Agents of SHIELD spin-off show recently confirming that Bobbi and Hunter will be the leads (if it is actually given the green-light), I'm sure that the show has more than a few tricks up its sleeves yet.