Captain Shaw is injured and transfers command to Riker, telling him he got them into this mess, he will get them out of it. Riker continues the strategy of hiding in the nebula while they repair the warp drive. Unfortunately, the Shrike is somehow able to keep finding them, and prevents them from leaving the nebula with the stolen quantum tunneling technology. Picard urges Riker to turn and fight, but Riker insists on getting the ship and crew home, safe. Jack realizes they're somehow leaving a trail the Shrike can follow, and breaks Seven of Nine out of her quarters (not sure why she's restricted to her quarters in this episode when she wasn't in the previous episode) to find the cause. Turns out their warp coils are leaking verterium as a result of sabotage. Jack is attacked by the saboteur, a Changeling. Seven saves him but the gas from the leaking engines nearly kills him. With the leak stopped, the Titan-A attempts to escape, but the Changeling sets off a bomb, once again disabling warp drive. Out of options, Riker finally listens to Picard's advice to fight, but the Shrike is still one step ahead, using the portal technology to have the Titan-A fire upon itself. The disabled Titan-A drifts into a gravity well at the center of the nebula. Riker tells Picard to remove himself from the bridge for getting them all killed. I don't really understand the hostility between Riker and Picard in this episode. They keep butting heads as to what action to take, and while their roles are reversed from what they're used to, much like Beverly, I just don't buy the animosity between them.
In the b plot... Worf fills Raffi in about a man named Titus who paid Sneed to lie about the sale of the weapon. They apprehend Titus and Raffi believes he is suffering from withdrawal while interrogating him. But Worf recognizes he's another Changeling, and needs to revert to his liquid form. Worf explains Odo told him a group of Changelings left the Great Link. The rouge Founders believe they shouldn't have surrendered following the Dominion War and are seeking revenge against the solids that defeated them. With everything about their plot being masked in misdirection, they conclude the stolen quantum tunneling technology itself was a misdirection, and that something else was stolen from the Daystrom Institute... (I'm guessing this is where Lore and Molarity will come in).
Some other Trek news... it was revealed today season 5 of Discovery will be the final season of that series.