It's amazing to me how much they were able to squeeze into this episode...SPOILERS AHEAD!
So we pick up Discovery with a captain and crew who have no idea where they are and after a little effort we find out it's the Mirror Universe. I love a good mirror universe story because it reminds us that the peace and harmony the Federation enjoys was hard earned and didn't come easy. Here in this universe Burnham is assumed dead, Lorca is a fugitive on the run, and Capt Tilly runs Discovery with an iron fist. (which makes for some great comedy)
While Ash and Burnham get closer we find out Ash is having major mental issues leading him to Lrell in the brig. She uses a Klingon prayer to either bring up memories or a hidden personality. Many seem to believe this is Voq altered to look human but I'll let the story keep it's secrets and unfold as it should. This freaks out Ash and leads him to Dr Culber to run tests on him. I don't want to give away the episodes big twist but it fits as Culber is so worried about his catatonic partner (Anthony Rapp) that he doesn't see the threat right in front of him.
As we get into the final part of this episode we have Burnham and Lorca going on a secret mission to the mirror version of USS Shenzhou. There are some wonderful fight scenes, perfectly timed slow clap, and even the agony booth!
Long Live the Empire and Long Live Star Trek Discovery!