Ever-terse, no-BS Admiral Nechayev (Natalija Nogulich) comes to the Enterprise and relieves Picard of command, putting him, Worf, and Crusher on an urgent mission of the utmost secrecy. Nechayev gives even-more-terse and even-less-BS Captain Edward Jellico (Ronny Cox) command of the Enterprise over Riker, on the basis that Jellico has long experience dealing with the Cardassians, who are figuring into a crisis that looks to be edging to the precipice of war. Jellico has his own ideas on how the Enterprise should be run, and wastes no time in seeing his changes implemented.
"Chain of Command, Part I" takes the TNG status quo and shakes it up in a way few TNG outings have attempted (among them "The Best of Both Worlds" and "Redemption," both of which also dealt with major military crises and personnel shifts). Jellico takes over and immediately has a laundry list of changes, like going from a three-shift duty rotation to four with less than a day's notice. Riker and Geordi are understandably frustrated, but Jellico will have none of it; he replaces the tenor and inclusiveness of Picard's "Make it so" with the rather simplistic and inflexible "Get it done." Jellico isn't incompetent or an idiot, which is a crucial point here (indeed, his battle-ready no-nonsense persona might be necessary if the Enterprise has to be on the front lines of a new war, and his "good cop, bad cop" maneuvers with the Cardassians offers a line into his thinking). But he's definitely not a people person, and he's especially skeptical of Riker as a first officer.
For me, the true fascination of this episode is just watching how Jellico operates and how the crew responds to it. After years of being accustomed to Picard's command style of consensus, Jellico represents a hostile takeover. My favorite scene might be the one where Troi tries to play psychologist and soft-pedal Jellico into taking a more morale-centric position with the crew. Jellico instead assigns her the job of taking charge of the "morale situation" herself, then deals the parting blow: "By the way, I prefer a certain formality on the bridge. I'd appreciate if you wore a standard uniform when on duty."
And I love how quickly Data becomes Jellico's go-to guy amid all this. Why? Because Data will give him, without hesitation or hedging, the facts of what is and is not possible, without pesky things like human fatigue and previously expected workday routines getting in the way.
Because the episode spans two parts, the story has the necessary room to breathe and explore the character dynamics before the meat of Picard's mission is unveiled. (I appreciated the scene where Riker considers taking his troubles with Jellico to Picard, but then decides against it when he sees how exhausted Picard is from the grueling training for the secret mission.) The mission involves Picard, Crusher, and Worf being sent to infiltrate what's believed to be a secret Cardassian facility manufacturing a terrible weapon of mass destruction. (A dialogue scene explains the stakes, and announces the Cardassians as major players in the Trek universe. On the other hand, I really could've done without the Ferengi middleman, who comes across as unfortunate — and implausible — padding.)
The would-be Cardassian WMD facility turns out to be a trap designed to lure Picard into capture, which is the subject of part two. But part one shows how energizing to the storytelling a command shakeup can be.