This Article Contains Spoilers - WARNING: This article contains major spoilers. If you do not wish to know vital information on plot / character elements in a story, you may not wish to read beyond this warning: We hold no responsibility for any negative effects these facts may have on your enjoyment of said media should you continue. That is all.
Jack-Be-Lucky is a member of the Brotherhood without Banners, an outlaw organisation founded by Beric Dondarrion to bring justice to the Riverlands after it is attacked by the Lannisters. It becomes a center for war after Robb Stark arrives in the Riverlands, and after his father Eddard Stark's death at the order of the Lannisters' King Joffrey Baratheon, being proclaimed King in the North.
Jack-Be-Lucky has only one eye and has spent time in Riverrun's dungeons. Lord Piper's bailiff hanged his father, his brother Wat was sent to the Wall and the Lannisters killed the rest of his brothers.
Another member of the Brotherhood, the Mad Huntsman, catches Sandor Clegane "the Hound", whose brother Ser Gregor Clegane, "the Mountain that Rides", is among the Lannisters' forces. Before he can put Sandor in a crow cage the Brotherhood make him agree to bring Sandor before Beric, who is in the Hollow Hill. Jack accuses Sandor Clegane of killing his brothers Lister and Lennocks, as part of the Lannister forces. In a trial by battle Sandor defeats Beric and is released, though his gold is confiscated.
At a Septry, the Brotherhood, including Jack, with Arya, encounter a band of Brave Companions, a vile sellsword company who originally fought for Tywin but have turned their cloaks to the Starks. Jack is among the members who search the Septry for captives. He finds hiding under the stairs the leader of this band of Brave Companions, Septon Utt, a pedophile rapist and murderer. The Brotherhood hang him and the other members for their crimes. Anguy and Jack then play dice, but no matter what game they play Jack has no luck. Gendry then asks to join the Brotherhood, saying he can smith for Beric. Jack tells Beric they need their mail mending. Another Brotherhood member, Lem Lemoncloak, tells Gendry he'll end up executed if he joins them, but Gendry says the same will happen for them. Jack says the crows await them all and they have need of Gendry's service, so Beric should take Gendry. Beric agrees and knights Gendry as Ser Gendry of the Hollow Hill.
In what becomes known as the Red Wedding, Robb Stark, his mother Catelyn Stark, and most of their army are massacred and Catelyn's brother Edmure Tully captured by their treacherous vassals, the Freys and Boltons, who have secretly joined the Lannisters. Catelyn is stripped and thrown in the river after a day and a night. Arya, while warging into her direwolf Nymeria, finds her mother and drags her out of the water. She is found by the Brotherhood and Harwin, the former Master of Horse at Winterfell, begs Thoros to bring her back. However Thoros claims she has been dead too long. Beric then performs the last kiss on her, and Catelyn rises, while Beric dies a seventh and final time. Leadership of the Brotherhood is taken by Catelyn, who becomes known as Lady Stoneheart. Stoneheart's mission, to take vengeance on all those she believes connected to the Lannisters, leads the outlaw band to fracture. Jack remains and is among the outlaws who hang Petyr Frey. When Merrett Frey comes with the ransom he asks which is Beric Dondarrion, Jack introduces says its him, and Lem says he's a liar, it's his turn to be Lord Beric. The outlaws decide to hang Merrett for his role in the Red Wedding, Jack bringing the rope and putting the noose round Merrett's neck. On Stoneheart's orders Lem hangs Merrett.
Petyr's brother Black Walder Frey leads hounds and hunters into Hag's Mire. The peasants speak of a one-eyed man, another wearing a yellow cloak, and a woman, cloaked and hooded.
When Brienne of Tarth, Podrick Payne and Ser Hyle Hunt arrive in the Riverlands looking for Sansa Stark and Arya Stark, Jack is among the Brotherhood who capture them. Brienne, Podrick and Hyle are brought before Lady Stoneheart. On finding that Brienne is apparently with the Lannister regime and thinking she betrayed her, Stoneheart tells her to kill Ser Jaime Lannister or be hanged. When Brienne refuses to make that choice, Stoneheart orders the Brotherhood to hang her and her companions. Jack-Be-Lucky takes her outside with Lem to hang her. When Brienne asks them to return her bones to her father Lem tells her he wants his wife and daughter back, and Jack tells him to get on with the hanging. However as they begin hanging her Brienne shouts a word. The Brotherhood release her and later she meets Jaime and tells him to come with her.