I really enjoyed this episode, it was a real punch to the gut when I worked out Grey was going to die and would be the previous host for Adira's symbiont. I think Grey's appearance at the end is interesting, we've certainly had glimpses into what that relationship is like for a joined person. This is another level and explores that more, and can easily be explained as a result of the trauma. If I followed correctly, Grey's joining was recent and he and Adira were still adjusting to it, so there may well be a sense of loss for the symbiont to know a being so entirely for such a short time. To then join with someone who knew and loved that last host, it's not a surprise that's something that would manifest itself. I think that's a very sad, very beautiful thread to Adira's story. They watched their love die, and now possesses his memories of his love for her as well as her own memories of the same time.
I'm really liking this new more liberated Michael, and she's much more relatable to me now (but that's a long story. Give me a phaser with a stun setting and don't answer my questions, and you'll find out

). It made sense to me that she didn't call for back up, she's been working without much of a net for the past year, just her and Book.
The crew PTSD storyline was great, and struck a lot of chords with our real life sci fi movie we're all going through. We definitely need to hear a lot more from the rest of the crew and flesh out those characters more. I am a bit worried about Saru though. He's lost his fear, but has he lost all sense of caution? He just decides it's probably the sphere data asserting itself, and never considers that some remnant of Control may have survived and is taking over the ship? Bad Captain, Picard would have ordered Geordi and Data to have done a manual diagnostic of the computer and look for any sign of Control, just in case. Mind you, Picard wouldn't have been asking the computer for advice in the first place, he'd just have held his crystal for a while and sipped Earl Grey.