This episode is celebrated as having the the longest opening teaser in the whole Star Trek Cannon. Fourteen minutes. (I got that little snippet from Memory Alpha after wondering why I had nodded off a couple of times).
A great deal of effort has gone into establishing a different atmosphere here in the Mirror Universe where Michael Burnham is strutting around pretending to be her evil-twin Terran equivalent while her Captain faces the prospect of a trip to the agony booth.
We have the moody, subdued lighting, languid bathing scene and slinky lingerie so Michael Burnham can indulge in the obligatory Mirror Universe recreational use of a junior crew member before getting into her gold-plated uniform.
We watch a "spacing" execution and MB, who is apparently captain over here, volunteers herself for an away mission to infiltrate the rebel base and gather intelligence rather than blasting them from high orbit.
Meanwhile, back on Discovery - at least I think that is where we are - A gold-encrusted Cadet Tilly is defending Commander Stammets from the widespread belief that he was responsible for the death of Doctor Culber. The multiple subterfuges and confusing character swaps currently taking place in this episode cannot eliminate the fact that NO SURVEILLANCE OF ANY KIND appears to have picked up Ash Tyler snapping the Doctor's neck.
Time for a well-earned cup of tea. What do you mean, the main part of this episode hasn't even started yet?