The Walking Dead season ten premiere is titled "Lines We Cross". The episode begins in space with an old Soviet Union satellite hurtling to earth. The first card states "Training Day". A grotesque walker with a piece of timber wrapped around its innards emerges from the ocean. It's killed by Judith (Cailey Fleming), who returns to the beach and joins a battle phalanx led by Aaron (Ross Marquand). They have shields with spiked fronts linked together. The Alexandrians and Hilltop characters march behind them. Daryl (Norman Reedus) observes as they approach a derelict ship.
As Lines We Cross begins, Jerry (Cooper Andrews) and Ezekiel (Khary Payton) open a metal door and let a few walkers escape. Aaron screams "archers", a volley of arrows kills them. Jerry and Ezekiel open the door again to let out more of the undead. Ezekiel orders "spears". They close ranks behind the shields and spear the walkers from below. Alden (Callan McAuliffe) launches a spear through a walker's head.
The door is opened again. More walkers are released. "Open ranks", Michonne (Danai Gurira), Magna (Nadia Hilker), and a much thinner Luke (Dan Fogler) emerge from the phalanx. They kill the walkers with their swords and maces. Jerry and Ezekiel can't hold the door. The remaining walkers pour out of the ship. Michonne commands "remember your training". The phalanx breaks into smaller groups. Daryl joins in the attack. The walkers are put down with military precision.
At the Oceanside settlement, people are cleaning fish and doing chores. Luke flirts with Jules (Alex Sgambati) as they separate rope. Daryl and Michonne walk and discuss a successful training, "Tara would be proud." She's happy her children can see the ocean for the first time. Judith plays in the sand with RJ (Antony Azor) and Jerry's children. As they show each other seashells, Judith is horrified to see RJ has found a Whisperer mask.
The second card says "Skin". In the Oceanside radio room, Aaron reports the find and orders Alexandria "to go on lockdown". Michonne countermands that. She wants everyone to be on the alert. Aaron disagrees, "No one saw Alpha's herd leave." Michonne will take a group to investigate. Daryl will catch up later.
On horseback, Michonne and her group split up to search. Aaron asks if they "are the villains" in someone else's story. A radio check reports nothing. Aaron races to a bridge to confront walkers. He's overcome as one bites his metal hand. Michonne comes to his rescue. She chastises him for being "stupid". They agreed not to cross their borders. She lost Rick on a bridge. Aaron is tired of keeping "his cool". He doesn't want to be the "nice guy" anymore. Jesus and Eric are dead. Michonne reminds him they have to be "smart" to keep their people alive.
Yumiko (Eleanor Matsuura) calls on the radio. They meet her group at an abandoned campsite. Magna leads them to several bodies. They see a walker skin on the ground. The riders return to Oceanside. Michonne worries that "fear will drive them apart again". She knows they are "the good guys". They must never question that.
Michonne watches as Judith tells RJ the story of the brave man on a bridge, who blew himself up to save his friends. Michonne gets teary-eyed when Judith says, "The brave man went to heaven". She embraces her children. RJ wonders about his dad. There's a loud boom as the satellite comes hurtling through the atmosphere above. Eugene (Josh McDermitt) wants to talk to her on the radio immediately.
The third card says "Bird Wisdom". We flashback to Aaron alerting Alexandria about the walker skin. In Alexandria, Father Gabriel (Seth Gilliam) wonders if "they are back". A montage follows of Rosita (Christian Serratos) working out to funk music while Eugene takes care of the baby. He has charted and graphed all of the baby's habits. Coco cries when he turns off the music. Rosita promptly turns it back on and Coco is soothed. Eugene is careful to make a note.
Eugene shows Siddiq (Avi Nash) his data on Coco. Siddiq promises to use some of the info. Gabriel comes in with a worried look. In the schoolhouse, Lydia (Cassady McClincy) struggles to read. Gabriel and the council come in. They need the room to discuss urgent matters. Lydia goes outside to practice with her staff. Negan (Jeffrey Dean Morgan) is picking tomatoes with a guard watching. He inquires what "the big meeting is for?" She tells him "someone found a skin." Negan tells her "to watch her back."
Siddiq puts Coco in her crib, then suddenly suffers a flashback. He reels as Alpha (Samantha Morton) and her Whisperers kill his friends at the stable. Dante (Juan Javier Cardenas), a new doctor from the Hilltop, wonders if he's "cool." He's reorganized the meds, then casually says, "We're like gods". Dante asks what's a "yellow alert". What's with "this Whisperer thing?" Siddiq continues to remember the massacre.
Gabriel visits Negan in his prison cell. Negan wants to "baby bird some of his wisdom in that pretty mouth." He knows people are putting on "their shitting pants" again. He advises Gabriel to keep the truth under wraps. When Gabriel leaves, he orders everyone to lock the gates for the night and double security at the walls. Everyone looks up as they hear the sonic boom and see the satellite streak across the sky. Eugene runs to the radio and calls Oceanside, "Something of grave importance is about to happen."
The fourth card says "Sea Dogs". We flashback again to Aaron reporting the skin on the radio. Daryl and his dog walk on the beach towards Connie (Lauren Ridloff) and Kelly (Angel Theory). Kelly is losing her hearing. Daryl signs with Connie. He's been learning sign language.
Daryl and Ezekiel wait on a dock. Connie approaches with dog. She writes that Daryl signs with a "southern accent". A fishing boat moors. Carol (Melissa McBride) jumps off and quickly embraces Ezekiel, before leaving with Daryl. They walk through the settlement. Daryl hasn't heard from her in a while. She went to the place where they pick up Maggie's letters, but found nothing. Daryl knows she was looking for Alpha. He tells her they found a mask. She doesn't want to help search.
The fifth card says "New Mexico". Daryl takes Carol on a motorcycle ride. They go hunting and shoot a deer. They track it to a Whisperer border. Daryl refuses to cross over. Carol watches as walkers devour the deer, "It could have fed 200 people." They sit together and talk about leaving. Daryl calls her his best friend. Carol wonders if it's just one fight after another. Daryl thinks people like them have to out there. They can just ride away, go to New Mexico. The fantasy is broken as they hear the satellite.
The sixth card says "Lines We Cross". That night everyone has gathered with fire fighting gear. Magna says it's war if we cross their border. Diane (Kerry Cahill) warns her that the fire will destroy Oceanside and then everything else. The forest is ablaze as they make it to the downed satellite. Everyone works feverishly to clear a fire line. Flaming walkers are killed. They set a reverse fire to burn the brush. Buckets of water are passed hand to hand. Ezekiel is almost overcome by smoke.
The final card says "Embers". More walkers attack them. It's a fight between the fire and the undead. Carol slits a walker's throat and uses the blood as an extinguisher. Daryl knocks down a tree with an ax to stop the walkers. The fire is put out. Michonne says to leave the Whisperer territory immediately. Eugene wants to save the satellite. She orders everyone to help him. She gives them ten minutes.
Carol and Daryl leave the others. They go to the cliff overlooking where the Whisperers kept their herd. Daryl asks Carol to stay. He walks away to give her a moment to think. Carol looks into the distance, and sees Alpha emerge from the tree line. The episode ends with them staring at each other with burning hatred. The Walking Dead returns next week with "We Are the End of the World" on AMC.