First of all, Cumberbatch was an awesome Dr. Strange. The movie began with Cumberbatch in his basement laboratory preparing a time machine to go back to the early 1990s. The time machine looked similar to the one in H.G. Wells' novel; it was very old-fashioned looking. As Dr. Strange is making the final preparations to go back, Mystique sneaks into the laboratory and manages to hide on top of the time machine just as Dr. Strange starts the time travel process, and she gets sent back along with him.
Back in the 1990s, Dr. Strange goes to Washington, D.C. since that's where the villain of the movie is hiding amongst a rich political family. They did a great job of portraying Washington, D.C. in the 1990s, by the way. There are CVS stores everywhere and run-down pay phones on the streets. Anyway, Dr. Strange goes to this political family who happen to be having a grand birthday party for their only son. The family lives in an elite apartment building for the super rich in downtown D.C., and Dr. Strange finds it necessary to disguise himself in order to get past the doormen and into the penthouse apartment where the family resides.
The party is a huge affair, and Dr. Strange manages to fit in by pretending to be one of the entertainers. During the party, hundreds of dancers, acrobats, and animals are paraded around and perform their various entertaining feats. Several of these entertainers are dressed like Dr. Strange in the comics, which I thought was a nice Easter egg. As Dr. Strange tries to track down the villain in all this party chaos, Mystique (who has been following Dr. Strange this whole time) sees her baby-self laying on a table in a corner of the apartment. She goes over and touches her baby-self's forehead, instantly causing her adult-self and her baby-self to vanish from existence due to the time paradox.
This is where the movie ended, most likely setting it up for a sequel.
