In the alley where Nicholas and Glenn tumbled off a dumpster into a herd of walkers, Glenn lies pinned underneath Nicholas' body as walkers disembowel it. Eventually, Glenn squirms to safety underneath the dumpster, stabbing at the walkers reaching for him until their corpses block him in.
Days pass as Glenn waits for the herd to move on. Finally, he crawls out and searches for water. "Heads up," says a voice, moments before a water bottle hits the ground. It's Enid, who tells Glenn that Alexandria was attacked, but runs away before he can question her further. Glenn chases Enid into the street but loses her.
Rick joins Maggie at the lookout post, where she anxiously scans the horizon for a sign from Glenn. Rick proposes that they lure the walkers away from Alexandria so that Glenn and the others can safely return.
Meanwhile, Glenn discovers David -- the Alexandrian who died at the fence and has now turned -- and stabs him through the head. Nearby, he finds the farewell note that David wrote to his wife, the note that Michonne said that he would not need because he would make it. He starts to head back to Alexandria but at the last minute, has a change of heart and goes after Enid.
Back in Alexandria, Gabriel posts a sign for a prayer circle. Rick shreds it as he strides by Gabriel, who patiently replaces it with a new sign.
Rick and Carl teach Ron how to use a gun. Rick stresses the importance of waiting for the right moment to shoot and not having your finger on the trigger until you are ready to shoot. He gives Ron an unloaded gun but refuses to let him actually practice shooting.
Morgan is on his way to the infirmary when Rick flags him down. Rick, Michonne and Carol confront Morgan about his refusal to kill Wolves during the attack. Morgan maintains that "all life is precious" (what he told Daryl in "Conquer") and that bad people are capable of changing. "Making it now," Rick challenges, "do you really think you can do that without getting blood on your hands?"
"I don't know," Morgan admits.
On the porch, Rick and Michonne come up with a strategy to lure the walkers away from Alexandria. Michonne urges Rick to enlist the Alexandrians' help executing the plan, but Rick is unsure. Then Deanna joins them and excitedly reveals plans for an expansion of the community telling them that there will be an after.
Rosita offers machete lessons to a group of Alexandrians. Eugene attends, but recoils at the weapon and admits he's scared of dying. Rosita gruffly tells him that dying is easy — what's hard is letting your friends die because you were too scared to save them. Eugene walks away while Rosita continues on with her lesson.
Meanwhile, Glenn finds Enid hiding in a restaurant and orders her to return to Alexandria. Enid points a gun at him but begrudgingly complies when he wrests it away from her.
In Alexandria, Rick saws wood to build new supports for the wall. Tobin joins him. As they are sawing wood, Tobin sees the crack in the wall shown before. Rick assures Tobin the wall will survive as long as they shore it up. Tobin admits that residents had been reluctant to change, but acknowledges that Rick has been right all along. "Don't give up on us," Tobin urges.
Glenn and Enid find green balloons left over from Rick's walker-herding mission. Enid suggests they use the balloons to distract walkers. Glenn directs her to a bush showing more balloons and a helium tank. As Enid inflates more balloons, Glenn lectures her against acting rashly out of fear. "We don't have to talk." Enid says harshly.
In the pantry at Alexandria, Ron knocks over items to distract Olivia so he can steal bullets from the armory.
Glenn and Enid finally arrive at Alexandria and find it surrounded by walkers. Enid's mood sinks but Glenn insists they move on.
Meanwhile, Spencer shimmies over the wall along a rope he's attached to the watchtower with a grappling hook. Rick screams at Spencer to turn back, in which he doesn't. Tara and Eugene notice that the rope is slackening, and Eugene goes for help. As the rope loses it's grip, Spencer is dropped in to the herd. Tara hangs off the wall shooting at walkers while Rick, Tobin & Morgan pull Spencer up to safety.
Rick chastises Tara for endangering her life (yet again) to save an Alexandrian, and then turns his rage on Spencer. Spencer explains that he had intended to find a car to draw the walkers away from the wall. Rick orders Spencer to come to him before executing any future strategies.
At the infirmary, Denise is curious when Morgan stops by to ask for antibiotics. After some probing, he admits that they are not for him.
Carol suspiciously watches Morgan lead Denise to the townhouse with the jail cell (in which Owen, the leader of the Wolves is being kept). She heads to Jessie's house and asks if she can watch Judith while she takes watch. She hears Sam call down to her from upstairs, asking if the people who attacked them were monsters. "If you kill people, do you turn in to one of the monsters?" he asks. Carol says that killing is the only way to keep from becoming a monster.
At the townhouse, Carol unlocks the door but Morgan stops her. She demands to know who Morgan is holding in the cell.
Meanwhile, as Carl is walking down the street, Ron quietly follows behind him, his gun in hand.
As Rick and Tobin shore up the wall, Rick sees Tara and apologizes for yelling at her. Deanna thanks Rick for saving Spencer, but Rick demurs and says that she should be thanking Tara. Deanna replies in saying that she already did. Rick then tells Deanna that he could have jumped off the wall, get a vehicle and Spencer would be dead by now, but Deanna remarks that he didn't do so and asks why he saved Spencer instead. "Because he's your son," Rick says. "Wrong answer," Deanna replies.
As Maggie is on watch, she sees the balloons that Glenn and Enid had to distract the walkers float in to the sky. She runs to Rick saying that it is Glenn, her hope restored.
However, as this happens, the watchtower topples over, crashing in to the perimeter wall.
- Jay Huguley as David
- Mandi Christine Kerr as Barbara
- Katelyn Nacon as Enid
- David Marshall Silverman as Kent
- Michael Traynor as Nicholas
- David (Zombified)
- Last appearance of Nicholas. (Voice/Corpse)
- Last appearance of David. (Zombified)
- After being removed from the "Starring" section in "Thank You", Steven Yeun is relisted in the opening titles.
- This episode also sees the return of Enid after last appearing in "JSS".
- Spencer traversing through the rope and almost falling into the herd is adapted from Issue 81 of the comic series.
- The title comes from Enid telling Glenn "heads up" after tossing a water bottle down to him.
- Another term for the title heads up is when everyone looked up to witness the tower falling down.
- This is the first episode of Season 6 not to feature a living character's death.
- This is also the first episode of Season 6 not to feature a new character.