Part One: Bravedog
Keeva, a blue greyhound, gives birth to four pups. There are three girls and one boy; she names the girls Eena, Nessa, and Brid, and names the boy Furgul. They are raised to believe that they are pure greyhounds, but as they get older, Keeva tells Furgul that he must run, because he is really a lurcher, and because of how fast he is growing, Dedbone is going to find out and kill him. Keeva also tells him that he must find his father, Argal. Furgul promises to come back and save Keeva.
When it is the first day in racing season, Keeva is supposed to be placed in a cardboard box to go off to the racetrack. She plans to run away before her leash can be put on, giving the dogs time to jump into another, empty cardboard box and go to the racetrack, where they can escape. However, the Gambler finds them and furthermore notices that they are not greyhounds. Dedbone goes and gets his shotgun, and while he does, Furgul manages to help Brid escape. The other three are still in the box, and Dedbone shoots multiple times until Furgul manages to tip the box enough to fall out of the truck.
Eena dies immediately of her shotgun wounds, but Furgul was only hit in the leg and Nessa still manages to survive. Nessa and Furgul go to a cavern, and Furgul hunts for them. They plan to survive in the mountain, but a day later Nessa dies of her wounds, leaving Furgul alone. He feels her spirit leave and imagines that now she will help all spirits find their way in the mountains. He then leaves the mountain to follow the river, where he meets Gerry, who takes him home. After a bit of nagging from his wife Harriet, Gerry manages to convince her to keep Furgul, who meets up with Kinnear, a bulldog.
Part Two: The Dog Who Runs in Darkness
Furgul learns from Kinnear all of the rules of the household, which he disapproves of. He plans to escape. One day, Gerry and Harriet take Furgul to the dog park. There he meets Samantha, a pitch-black German Shepherd that shares his interests. They play-fight, but the owners don't understand and think that they are attacking each other, so they pull the dogs away from each other. Before they are taken away, Furgul learns that Samantha's real name is Dervla.
After the incident at the park, Gerry and Harriet don't want anything like that to happen again, so they decide that it's time for Furgul to get neutered. When Kinnear tells him what neutering really is, Furgul knows that he cannot let that happen and plans even more intently to escape. When they finally take him to the veterinarian's office, he bolts as soon as they take off his collar and doesn't look back.
Out on the streets he meets Pace, a Labrador Retriever and seeing-eye dog with an overwhelming sense of sarcasm. Pace tells him to go through the mall, but watch out for the guards. While there, he also meets eight miniature female dogs who fall madly in love with him and chase him through the mall. The chaos confuses the guards, though, and gives him the opportunity to escape.
As soon as he exits the mall, he gets captured by "The Traps", or the dogcatchers. While in the truck on the way to the animal shelter, he meets Zinni the papillon, Tess the beagle, and Skyver the mutt. The truck stops once again to get another dog, who turns out to be his father Argal. There, he learns that unlike the others, Argal isn't going to be given his five days in the shelter. He has been labelled a dangerous dog and is going to be killed as soon as they get to the shelter.
While at the shelter, Furgul meets with Brennus, a Saint Bernard who taught Argal what he knows. Before Argal is killed, they give him some time with Furgul and with Brennus. While there, Furgul is told about how the mysterious Doglands are inside of you, and that his spirit will always be with them, and you just have to feel it. Then he is taken away, and Furgul becomes the new shelter leader, being Argal's son. So angered by the death of his father, Furgul decides to have a revolt. All the cage doors are opened and the dogs break free, refusing to go anywhere until their demands are met.
During the revolt, Furgul meets with Jodi, a dog whisperer, who offers that all the dogs in the revolt come live at Appletree Dog Sanctuary instead of going back. What makes Furgul agree is that she says he will be killed when they go back because he will be labelled a dangerous dog like his father. They all live at Appletree for a while until Furgul hears a whimpering pup. When he goes to help the pup, he gets captured by two thieves, Tattoo and Spotty, and finds out that the pup was only hurt for the sake of the trap and didn't know any better. He gets labelled "dogmeat" and is fed to Gremlin, Lunk, Freak, and Chopper. Dervla comes out of the shadows and kills them. Seeing the dogs dead, Tattoo and Spotty put him with Dervla, where she tells him their job is to distract guard dogs while the two humans go burglarising. At the first house, Furgul meets with two giant schnauzers named Cogg and Baz and convinces them to attack Tattoo and Spotty with the bribe of bacon. After the attack, Cogg and Baz join Furgul and the others.
Dervla, Cogg, and Baz come to live at Appletree, and peace is retained for a short amount of time. Then Furgul expresses his desire to save his mother Keeva, and Jodi says that she will look up the racing greyhounds on the betting page of the papers. Dedbone is not listed because that was just the dog's name for him, so Jodi asks racing names until something rings a bell. Furgul remembers his mother telling him her racing name, but he just can't remember. Eventually he remembers that it's "Sapphire Breeze", and he and all the dogs go to the racetrack.
Part Three: The Dog Bunch
While on the racetrack, Keeva is in the lead and has only a few steps to go before she would win, but then the spirit of Argal washes over the racetrack and she begins to dance with glee at feeling it. Soon all of the other dogs begin to dance and none of them finish the race. Afterward, Dedbone prepares to kill Keeva for her "little act" on the track.
A plan is formulated to save Keeva, but when Furgul sees all the other greyhounds shut in Dedbone's Hole, he figures that he must save them all. Then he finds out that Tic and Tac, the bullmastiffs in Dedbone's Hole, have pups. Zinni has experience walking on wires, so she agitates the greyhounds enough with her presence for Dedbone to open the gates to see what the matter is. Then, the greyhounds charge and the battle begins.
Cogg and Baz, now aware of their newfound abilities in killing, kill all five of Tic and Tac's pups, and then Tic and Tac are killed themselves by other dogs. Furgul sees Dedbone driving away with Keeva in the back of the truck and races after her. Brennus sacrifices himself to save Keeva, getting shot attacking Dedbone and then lying injured until the truck runs him over, finally killing him. Right before he dies, Brennus tells Furgul to run "The Doglines", the places where the ancestors of the dogs walked. Then Skyver lunges at Dedbone, knocking him back enough for him to tip over the side of the chasm and die there.
