[Originally aired November 12, 2017 on CBS All Access]

Starfleet orders Discovery back to Federation space and abandon the Pahvons to Klingon annihilation. Lorca sets a course at Warp 5 to give them a 3 hour window to figure out a way to stop the Klingons and figure out how to counter the cloaking technology.

Tyler suggests using the Discovery as bait and send boarding parties over to Klingon ships to plant sensors. Lorca approaches Stamets to make 133 spore drive jumps in order to gather the data they need. This is despite Culber finding evidence that the jumps are causing brain changes in Stamets.

Lorca coerces Stamets into doing the jumps by showing him the potential information they can gather that can be used for research after the war.

Tyler requests Burnham join him on the Klingon away mission and Lorca resists but is eventually convinced to let her go.

Stamets prepares for the jumps and Tilly accidentally lets slip to Dr. Culber that he's been experiencing side effects. Culber fits Stamets with a cuff to allow him to treat Stamets while he is in the chamber.

Tyler and Burnham beam aboard the Klingon ship and Discovery distracts the Klingons to allow them time to plants the sensors.

Burnham detects a human life sign and insists they rescue whomever it is. They find Admiral Cornwell as well as L'Rell in the death room. Burnham attends to Cornwell while Tyler goes into shock at seeing L'Rell. Burnham revives Cornwell but she can't feel her legs. Turning to Tyler, she shoots L'Rell and Tyler collapses. Burnham arms Cornwell and proceeds to the bridge herself to plant the sensor.

Once the sensors are active, Discovery starts its planned 133 spore drive jumps, causing the Klingon ship to cloak. Stamets' vitals start to spike and Culber wants Lorca to call off the jumps but Lorca orders him to keep Stamets alive to complete the mission.

When Kol orders the ship to jump to warp, Burnham reveals herself in order to prevent them fleeing before the sensors can gather all the data and addresses Kol as the killer of T'Kuvma. 

In the Klingon death room, Cornwell is talking Tyler out of his shock when the Klingons enter and Cornwell shoots. Tyler recovers and grabs a disruptor to fight.

On the bridge, Burnham challenges Kol to battle. 

The Discovery continues and completes its jumps and begins calculating the algorithm to unlock the cloak. Lorca is advised to jump away to safety but doesn't because the Klingons aren't firing. 

Saru completes the algorithm and sends it to the transporter room and they bring back Tyler and Cornwell. At the last minute, L'Rell revives and jumps Tyler and gets caught in the transport. On the bridge, Burnham continues to fight and is notified of imminent transport. She grabs Georgiou's com badge from Kol and jumps off the bridge catwalk just as the transporter grabs her. 

With the away team back on board, as well as Cornwell and L'Rell, Lorca orders that all photon torpedoes be fired at the cloaked ship of the dead and it is destroyed. Burnham turns and finds Tyler gone despite having entered the bridge with her.

Lorca debriefs with Admiral Terral. Cornwell is in surgery and expected to recover and the anti-cloaking algorithm is being refined for fleet-wide use. However, Klingon ships continue to advance on Starfleet. The war is not over. Terral orders Lorca and Discovery back to Federation space as Lorca is to be awarded an honour for his contributions to the war effort.

Burnham goes to visit Tyler and Tyler points out that Burnham achieved the mission alone. Burnham asks why seeing L'Rell triggered the extreme reaction it did. Tyler admits he's been have nightmares since escaping the ship. He credits L'Rell as his torturer, captor, and lover, the cause of his nightmares as well as the reason he's still alive. Burnham comforts him.

Lorca tells Stamets that he told Starfleet to give the medal to Stamets for making the jumps. He says they'll warp back to the star base but Stamets offers to make one more jump to get the crew back to safety. He explains that it really will be his last jump because he needs to find out what is happening to his brain. 

Tyler has a flashback of having sex with L'Rell and wakes up on his couch with Burnham asleep at the other end of the couch. He gets dressed and goes to see L'Rell in the brig where he asks what she did to him. She responds that she will never let them hurt him and warns him,"soon."

Stamets enters the spore drive chamber for the final time, having promised Culber they'll go to the opera once he's on medical leave. Something goes wrong in the jump. Stamets falls out of the chamber and murmurs about seeing all the permutations. On the bridge, Lorca wants to know where they are and Saru is at a loss as none of their navigation instruments seem to be working.