Warning: spoilers ahead for the Agents of S.H.I.E.L.D. Season 4 winter finale, called "The Laws of Inferno Dynamics."
Agents of S.H.I.E.L.D. spent the first half of Season 4 building up Eli Morrow as the big bad of the year, and it seemed likely that the midseason finale would revolve mostly around the Inhumans and Ghost Rider as they tried their best to take him down. "The Laws of Inferno Dynamics" did indeed spend most of the hour dealing with Morrow, but the biggest twist of the evening was all about Agent Melinda May. The final moments of the episode revealed that our badass Agent May has been incapacitated and replaced by an android.
May really didn't have a lot to do for most of the hour. She and Coulson went their separate ways early in "The Laws of Inferno Dynamics" as she headed to Dr. Radcliffe's lab to pick up AIDA and bring her along on the mission to stop Eli Morrow. When she arrived at the plane with AIDA, nothing seemed especially out of the ordinary. May pounded on some bad guys, AIDA built a portal to send a nuclear bomb to another dimension despite being shot by a minion of Morrow's, and the day seemed saved.
The kicker came when Director Mace sent Agent Nathanson back to Dr. Radcliffe's lab to repair AIDA's bullet wounds and gather the data for S.H.I.E.L.D. to study. Nathanson was shocked to open a door and discover the body of Melinda May, bloody and unconscious on the floor. He didn't have much time to react, however, because AIDA expressed her regret and snapped his neck. Then, the very last scene of the episode showed the main characters gathered in the S.H.I.E.L.D. common room...and a Melinda May about to share a drink with Phil Coulson.
It probably won't come as a huge surprise to Agents of S.H.I.E.L.D. viewers that AIDA turned out to be a danger to the agents. The Marvel Cinematic Universe proved that artificial intelligence is extraordinarily dangerous with the entire plot of Avengers: Age of Ultron, and Director Mace even name-dropped Ultron in the beginning of "The Laws of Inferno Dynamics." The odds were pretty good that building AIDA would turn out to be a pretty bad idea. Still, not many of us might have guessed that AIDA's first major act of aggression against humankind would be taking out May and replacing her with a May-bot.
A big question now is of when AIDA built her May-bot. She was seen constructing what looked like a brain at the end of the previous episode after reading the Darkhold gave her unnatural ideas. AIDA very well could have planning on building her own May from the first moment she opened the book. After all, May is a logical choice for AIDA to try and reproduce. AIDA spent a great deal of time with May while May was unwell, dead, and then recovering from being dead in Radcliffe's lab. The android would have a working knowledge of May's physical abilities as well as her personality. Honestly, AIDA might have just been really, really lucky that Mace happened to send May to fetch AIDA rather than a different agent that didn't already have a robo-doppelganger in a back room somewhere.
Hopefully the fact that the May-bot is so realistic means that AIDA is planning on keeping the real Melinda May alive as a source of information. I'd hate to imagine an Agents of S.H.I.E.L.D. without May on board. I can deal with sentient robots and an evil book with blank pages and a guy whose face lights on fire easily enough, but no May is no good.