The crew of the Discovery and the diplomats make a last-ditch effort to connect with Species 10-C and save Earth and Ni'Var from the DMA.
Tropes:
- Abandon Ship: With Federation HQ unable to move and the debris from the DMA getting closer, Admiral Vance orders the rescue efforts stopped and HQ evacuated while he stays behind to provide covering fire. Tilly ends up staying behind as well to help protect her students with him.
- Attack Pattern Alpha: Vance orders defensive formation Omega.
- Bittersweet Ending: While Earth and Ni'Var are damaged from the DMA's effects, they make it out of the worst of it and the crew of the Discovery are able to reach Species 10-C to stop the DMA. However, for his part in the worsening of the situation, Book is tried for his crimes, putting him on forced humanitarian aid for the foreseeable future. On the plus side, the Federation’s actions have spurred other planets into returning into the fold, with former founders Andoria and United Earth in talks, the latter wanting to return immediately.
- Book Ends: The beginning and end of the seasons have Rillak and Burnham discussing the idea of the latter joining the Voyager-J’s project. Unlike last time, Rillak tells Burnham she is more than ready, though Burnham still turns it down.
- The Bus Came Back: Tilly returns for the first time since "All is Possible".
- Call-Back: Reno still calls Stamets "Bobcat".
- The Cameo: Former Georgia House of Representatives Minority Leader Stacey Abrams appears near the end as the President of United Earth.
- Cool Starship: Federation HQ is a warp-capable starship in spite of its design, and every deck is capable of separating into an autonomous lifeboat in its own right.
- Crippling Overspecialization: The 10-C are completely incapable of stopping Tarka once he escapes, because the orbs are their only means of dealing with potential intruders. Engaging militarily with other beings isn't something they ever considered doing.
- Death Equals Redemption: Guilty over having essentially ruined first contact, Gen. Ndoye offers to pilot a kamikaze shuttle run that will disable Book's ship, knowing full well that it's a one-way trip. Subverted in that they are able to transport her out at the last second.
- Disney Death: It seems that Book may have escaped from his destroyed ship, but whatever power it had wasn't enough. Fortunately, the 10-C intercept his transporter signal and rematerialize him once his importance is explained.
- Explosive Instrumentation: Consoles explode all over the bridge of Discovery when they overload their spore drive, with at least one Red Shirt caught in the blast (survival uncertain).
- Gunship Rescue: The USS Mitchell arrives at Earth just in time to intercept an asteroid that was about to destroy an evacuation shuttle.
- Heroic RRoD: To escape the orb Discovery is trapped in, Stamets reveals a plan to overload the Spore Drive to destroy it. It works, but it completely obliterates the spore chamber and renders the drive inoperable until they can put in to spacedock— a trip which, on conventional warp drive, will take decades.
- Heroic Sacrifice: Quite a few. All of them are subverted in that they survive, which reviewers commented on.
- Adm. Vance elects to stay behind and use (what remains of) Starfleet HQ to buy Earth as much time as possible. Tilly chooses to join him.
- Detmer volunteers to fly the suicide mission... only to be diverted when Ndoye does it instead. Ndoye is then beamed away at the instant of impact, leaving her severely wounded but treatable.
- Tarka diverts all remaining power from Book's ship to beam Book out before they impact the hyperfield. He then uses his universal transporter, figuring a long shot is better than just dying. Whether it worked is left ambiguous.
- Homeworld Evacuation: The DMA threat forces the evacuations of Earth, Titan, and Ni'Var. Unfortunately, there's nowhere near enough capacity to save even a small fraction of each planet's population. Fortunately, Burnham and Book convince Species 10-C to stop the DMA, saving the aforementioned planets.
- Just in Time: Double Subverted. Tarka transports Book to Discovery moments before his ship impacts the hyperfield, but Book fails to materialize. The 10-C then reveal they intercepted the transport, materializing Book once Burnham explains his importance.
- My God, What Have I Done?: Ndoye realizes she made a big mistake when she is told that her venting the plasma last episode could have jeopardized everything.
- Mythology Gag: Among the ships involved in the evacuation efforts are the USS Yelchin the USS Nog, and the USS Mitchellnote
- The destruction of the spore drive presents the possibility of Discovery needing to make her way home via warp drive, much like another famous Starfleet ship.
- The Needs of the Many: Knowing they need to stop Tarka and Book, the decision is made to send someone out in a shuttle to ram Book’s ship. Detmer stands and nominates herself, much to Owo’s horror, but Ndoye steps in instead.
- No Ontological Inertia: When the DMA is deactivated, all the debris it sent flying at Earth and Ni'Var immediately reverses course, as if being drawn into a massive gravity well as opposed to being propelled by one; though it's likely that Species 10-C deliberately engineered this to prevent any further damage.
- Poor Communication Kills: As it turns out, Species 10-C has no concept of individualism, something that T'Rina comes to realize after her mind meld with the 10-C, so the contradictory actions of Discovery and Book's ship confuddle them. Once everything is settled, the diplomats and the bridge crew come down to their home and help explain everything.
- Psychic Nosebleed: T'Rina gets one when she telepathically contacts the 10-C.
- Replacement Goldfish: Tarka attempts to invoke this with Book, telling him he can come with him to Kayalise, where Kwejian will still exist and his family will be alive. However, Reno immediately points out that they won't be his Kwejian or his family, nor will her wife be there. Book agrees with her.
- The Reveal: Species 10-C is finally revealed... and they are giant creatures.
- Rousseau Was Right: The 10-C agree to stop using the DMA once they understand the harm it causes.
- Suicide Mission: With no weapons and no other means of stopping Tarka, Ndoye suggests ramming Book's ship with a shuttle to disable it. However, the shuttle will have to be flown manually due to interference that will throw off the autopilot, and transporters are at best spotty close to the DMA's power source. The task at first seems to require Detmer's skills, but Ndoye offers herself because she has plenty of experience and will gladly sacrifice herself to save Earth. Luckily, Discovery manages to pull her out, injured but alive.
- Trash the Set: The Spore Drive room goes up in a wonderful ball of flame and glass when the ship escapes from the orb, and the bridge of Book's ship gets heavily trashed before the entire ship goes up.
- Uncertain Doom: Did Tarka die or did he manage to arrive in the alternate universe?
