After dying, Jake arrived at a way-station in the middle of the Mohaine Desert in Mid-world, and spent many weeks alone in the way-station, his memory of who he was and how he died fading little by little in the erratic time of All-world. Later, he was found by Roland Deschain, who chanced upon the way-station, nearly dying of thirst. Jake took Roland into his care and gave him water and food, and Roland then hypnotized the boy into telling him where he came from and how he died. Roland took pity on the young boy and agreed to take him along on his journey to find the Man in Black, who Roland believed had somehow murdered Jake in his world.
When Roland and Jake finally caught up to the Man in Black in the caverns beneath the Cyclopean Mountains, Jake was nearly tossed off a crumbling, ancient bridge located deep underground, and he begged Roland to help him up. The Man in Black offered Roland the choice of either saving Jake or learning the truth, and Roland, desperate to find the Dark Tower and believing the Man in Black to know his destiny, allowed Jake to fall to his second death, a choice that would haunt him for the rest of his life. Jake's final words as he plunged into the abyss were: "Go, then. There are other worlds than these."
After Roland's confrontation with the Man in black, he descended to the Western Sea, and walked the shoreline, coming across three doors that opened into the minds of people on Keystone Earth. The final of these doors – marked "The Pusher" – led into the mind of Jack Mort, a serial killer, and Roland discovered in horror that it had been Mort who, in the guise of a priest (explaining why Jake had confused him witht he Man in Black), had pushed Jake in front of the oncoming car. Unwilling to watch Jake die again, Roland stopped Mort from pushing Jake into the road, causing a temporal paradox.
Due to Roland's interference with Jake's first death, both Roland and Jake (now alive in 1977) experienced the memories of two conflicting, co-existing timelines. Roland remembered both meeting Jake at the way-station and letting him fall, but alternatively recalls passing the way-station without meeting anyone. Jake experiences his death and passage to the way-station, as well as his journey with Roland and his second-death under the Cyclopean Mountains, but similarly experiences his own life in New York City, leading him to contemplate whether he imagined Roland. Both Jake and Roland realized that they were slowly going insane. In Mid-world, Roland, with the help of his new companions, Eddie Dean and Susannah Holmes, discovered a way to "draw" Jake out of 1977 and in Mid-world in order to join their ka-tet.
The moment he re-entered Mid-world, both Roland's and Jake's minds became stable again with the memory of meeting, and Roland promised never to let Jake die again. Jake often acted as the adopted son of the group, especially for Roland, whom he came refer to as Father. In combat and peril, Jake was as trusted and depended upon as the ka-tet's other members and rose to the responsibility ably. His childlike diversions and pet Oy provided some levity to the group, while his skill with the gun was equal to Dean's and comparable to Roland's, and his ability to think and calculate strategies like the other members of the ka-tet despite his age was impressive.
Due to the shortage of firearms the gunslingers faced at times, Jake was one of the first to embrace the "Riza" throwing weapon during The Battle of Calla Bryn Sturgis. The weapon resembled a dinner plate with a razor's edge on all sides, save for two inches spared for gripping it. Having shown both a quick aptitude and deadly precision (he was easily able to cleave an apple in half sitting on a full-grown person's head), Jake continued to carry them as a backup weapon even when the ka-tet eventually encountered more firearms. Roland later noted that Jake's battle cry when throwing the Rizas was every bit as ferocious as a gunslinger in the heat of battle, distinguishing the young man's professionalism regardless of weapon.
Jake eventually accompanied Roland to the Maine of 1999 in order to prevent the death of writer Stephen King in a car accident, and subsequently died himself when he leapt between King and Bryan Smith's oncoming van. Roland buried Jake in the forest off the road, and Irene Tassenbaum, who had happened upon the scene, promised to plant a rose on the grave. Jake is later reunited with Eddie, Susannah, and Oy in an alternate New York City, in which Eddie and Jake are brothers bearing the surname of Toren, and Oy is a dog with gold-rimmed eyes.