The book begins with Graystripe leading a daring rescue to save cats captured by Twolegs. The cats are in cages and being placed into the back of a van to be taken to an animal shelter. Graystripe's group manages to save all the cats but Brightheart. The van starts to move, so Graystripe knocks another cat who wanted to stay and save Brightheart out of it. Then he frees Brightheart, but he falls backward and the door slams, and he is trapped in the van.
The story cuts ahead a few days, and Graystripe is dreaming about how he first met Firestar. However, the dream changes into a nightmare of Graystripe in the midst of a raging inferno. He awakens to find himself still inside a Twoleg nest to which he had taken at least a quarter moon earlier. A shot of the van in the driveway, as well as the husband's appearance on the first page, reveal that the van driver took a liking to Graystripe and brought him home to be his kittypet. Graystripe, however, wants nothing of it, and he vows to escape as soon as the rain outside stops. One sunny day, Graystripe gets his chance, but when he runs outside the smells and sounds overwhelm him. He flees back inside, realizing that the Twolegs kept him in their nest too long and now he doesn't know which way is home.
The next day, Graystripe leaves the house again, but is attacked by a dog and a guy with a lawnmower. He runs back to his house, where he is put inside again. Luckily, he escapes through a window and starts to look for a way back to the forest. Unfortunately for him, the Twoleg nests seem to go on forever. While exploring, Graystripe meets Duke, a kittypet with a spiked collar who doesn't appreciate Graystripe's trespassing. Graystripe provokes a fight, but Duke defeats him due to Graystripe's fighting skills being rusty. Graystripe runs away from Duke, wondering if he's grown too soft.
As Graystripe flees, a kittypet in a tree calls out to him. She introduces herself as Millie, and tells him not to worry, because nobody has ever beaten Duke. Millie shows Graystripe back to his house, and he hopes that he gets to see her again. That night, Graystripe dreams that he is in StarClan, visiting his mate Silverstream and their daughter, Feathertail. The dream of them gives Graystripe the determination not to be a kittypet, and he takes advantage of his Twolegs' not having air conditioning by escaping through another window. Graystripe decides to find a guide to his surroundings, but two posh cats tell him that Millie hasn't been seen for a while. Graystripe scares off the posh cats and continues on his way.
A few days later, Millie shows up at Graystripe's house and takes him on a walk through the forest. It turns out she was on vacation, but now she's home. Graystripe talks about the Clans, and she is eager to learn more. In a training montage, Graystripe teaches Millie how to hunt and fight, as well as educating her on Clan lore. She says that the Clans sound amazing, like an adventure every day.
Duke and his cronies interrupt and attack Graystripe and Millie, but the duo use their fighting skills to defeat him. Millie tells Graystripe how amazing he was, and that he should rejoin his Clan. Graystripe says that he doesn't want to talk about that and brushes her off.
That night, Graystripe dreams again of Silverstream, who tells him that he should go and find ThunderClan. Graystripe says that he wishes he could be with Silverstream, but she tells him that he has a traveling companion. Graystripe wakes up and finds Millie, explaining that he is going to rejoin his clan after all. He asks her to come along, but Millie says that she can't her whole life behind. Millie heads home and wonders what to do.
Graystripe leaves and sets out on his journey, but he doesn't manage to find any food and is slowly starving to death. After six days, he collapses in a pipe and falls into a dream. He is surrounded by fire again, and sees the faces of his Clanmates staring at him. Suddenly, Millie wakes him up and brings him water and food. She explains to Graystripe that after he left, she decided to go with him, so she used every one of the skills he taught her. She then asks him who Silverstream is, because Graystripe mentioned her name while delirious. Graystripe tells Millie about Silverstream, and says that now that he's found Millie, he's not lonely anymore.
Millie tells him that she can get them to the edge of Twolegplace, but then it will be up to Graystripe. She asks if he's strong enough to make the journey, and Graystripe says that he thinks he is, but if he needs help he has her. Millie says that she'll always be there for Graystripe and the two head off on their quest.
Tropes appearing in this volume:
- Adaptational Attractiveness: In the books, half of Brightheart's face is destroyed due to a near-fatal encounter with a dog: covered in scar tissue, and she lost an eye and an ear. In the original black-and-white version of this volume, she's normal-looking except that one of her eyes is closed, making it look like she's constantly winking. Somewhat averted in the full-color re-release, where she's shown with scars covering one eye, though the damage isn't to the extent it's described in the books (she still has both ears, for instance).
- Alertness Blink: A "!" appears when Graystripe pounces on a beetle.
- Audible Sharpness: In one scene, Graystripe unsheathes his claws with a "snikt" sound effect.
- Bit-Part Bad Guys: Duke is one of these. His only reason for existing was so that Graystripe could fight someone in the first book, and out of all the villains in the series, he is one of the quickest to go down.
- Brawler Lock: During Graystripe and Duke's second fight, a panel features them locked in combat and snarling, forelegs pushing against the other, trying to pin the other down. Duke ended up coming out on top for a few moments, but Graystripe was able to turn it to his own advantage and win.
- Cabin Fever: Graystripe gets this, since he's lived outdoors in the forest his whole life and is now shut in a house as a pet. Results in him desperately searching for a way out and clawing up some of the furniture.
- Caged Bird Metaphor: When Millie's trying to decide whether to leave her owner and live in the wild, she looks at her owner's pet bird in its cage and wonders aloud, "Would you fly away from here, if you could?"
- Circle of Shame: Graystripe has a fever-induced nightmare that StarClan cats are surrounding him and screaming that it's all his fault that bad things happened to ThunderClan.
- Colorization: Graystripe's Adventure was originally drawn and released in black-and-white, in three different volumes. James Barry later colorized it and it was re-released as a single volume.
- Confused Question Mark: Graystripe has one appear above his head when he notices an open door in his house, and Millie has one toward the end when finding Graystripe.
- Crazy Cat Lady: Millie's owner - not so much due to the number of cats, because as far as we know she only has one, but because of the level of obsession. She's an elderly woman with cat toys everywhere, as well as a custom cat bed with Millie's name, cat pictures on the wall, and a cat calendar and refrigerator magnets.
- A Day in the Limelight: This manga trilogy serves as Graystripe's.
- Delirious Misidentification: When Millie finds the very sick and delirious Graystripe toward the end, he calls her Silverstream, the name of his former mate.
- Divided for Publication: The Graystripe manga trilogy was originally meant to be a single volume, roughly the same length as standard volumes of manga. Then someone decided that it should be released on the same day as the first book in a new series, but the illustrator wasn't done with it, so they decided to split it into three shorter volumes. Funnily enough it was later "un-divided" when the trilogy was reprinted as a single, full-color volume.
- Ear Notch: Duke has scarred ears, demonstrating that he's no stranger to fighting.
- Heroic Rematch: Graystripe's first fight with Duke ends with Graystripe running away with his tail between his legs. He defeats Duke the second time around, much to Millie's admiration.
- Names to Run Away from Really Fast: Titles: Duke is a minor antagonist who appears in this volume.
- Perspective Flip: The first scene is a scene that initially appeared in Dawn from Squirrelpaw's point of view; now we're seeing it from Graystripe's.
- A Pet into the Wild: Millie left her home to help Graystripe find ThunderClan and join it herself.
- Red Eyes, Take Warning: In the full-color version, one of the evil BloodClan cats attacking Graystripe in his memory has red eyes.
- Riding into the Sunset: The final panel shows Graystripe and Millie walking toward the sunset.
- Series Continuity Error: In Sunset and The Sight, it is mentioned that StarClan are unable to see Graystripe. However, Silverstream and Feathertail can easily see him (in fact, they visit him!) in this book.
- Second Love: Graystripe's first love was Silverstream: they were Star-Crossed Lovers, and she died giving birth to his kits. Many, many moons later - when his children are grown up and thinking about having their own kits - he falls in love with Millie.
- Shout-Out: James Barry revealed
◊ that the Twoleg who sprays Graystripe with a hose is a cameo of Patsy Stone from Absolutely Fabulous. - Sitting on the Roof: There's a scene where Graystripe and Millie have a heart-to-heart conversation on a random roof. This image was even colored and used in promotional materials.
- Teach Me How To Fight: Graystripe tells Millie all about his life as a ThunderClan warrior. She is so intrigued that she eventually asks him to train her to fight.
- Through a Face Full of Fur: Millie blushes when Graystripe thanks her profusely for showing him a patch of trees that reminds him of the forest. Even more noticeable in the full-color version, when it's colored distinctly pink against her brownish fur.
- Training Montage: There's a section where Millie asks Graystripe to teach her to fight, and it shows training sessions spanning several days, interspersed with her asking questions about Clan life, with Graystripe narrating over it about her progress.
- Unsuccessful Pet Adoption: Graystripe is caught by humans while trying to free his Clanmates from captivity, and is adopted by a family. Although he lets them pet him, his feral nature means that he's never completely at ease, and he scratches the furniture and shreds a toy at least once. Once he's let outside and gets over all the noise and smells of the city, he runs away with another pet cat to find his Clan.
- Worf Had the Flu: Graystripe is defeated easily by a kittypet named Duke. However, Duke defeated Graystripe so easily because he had been captured by humans and stuck inside a house for two months, leaving him out of practice.
