A Hidden Enemy is the second book in the Survivor Dogs series.
The story begins with a flashback. Yap (Lucky) and Squeak (Bella) are young puppies living with their mother and siblings. While in the yard, pretending to be a strong warrior hunting, Yap hears a strange howl in the distance. His mother informs him and his siblings that the howl is not a dog's howl, but a wolf's howl. She tells them of wolves and how they're not to be trusted. Mother-Dog tells of the mythical Nuzzle (better known as "Wildfire"), a curious pup who would have been killed by wolves if not for her grandfather Lightning saving her.
The next chapter skips ahead to Lucky hearing his Leashed Pack friends in trouble. Between being on his own and saving his friends, Lucky choses to run back and help them. It turns out that the pack has unknowingly invaded another pack's territory. They're a pack of forest-raised dogs known as the Wild Pack. This pack consists of: a wolf-dog alpha, a Greyhound beta, a large male known as Fiery, a small terrier-mix known as Snap, a brother and sister known as Spring and Twitch, a long-earred male known as Mulch, and a Pug omega.
This pack is intimidating even to Lucky, with their alpha and beta being especially so. The Leashed Pack doesn't have a chance against the wild dogs. In a burst of dumb courage brought on by noticing Lucky in the distance, the youngest dog Alfie decides to stand up to the alpha. Alpha has none of this and swats Alfie away with his paw, leaving a gaping wound in the young dog's side. At that moment a small earthquake hits.
Lucky is separated from his pack in the chaos and nearly killed by a falling tree. While separated, Lucky rescues the Wild Pack's beta from a crack in the ground. He recognizes her as Sweet, the dog he temporarily befriended in the city. Sweet doesn't know that Lucky is a part of the Leashed Pack and simply thinks it's a coincidence that they've met again. She offers him a place in her pack but he declines, insisting he's a Lone Dog. The two part ways and Lucky goes to reunite with his packmates.
Lucky finds his pack huddling together in a hollow. Alfie is with them but it's obvious that he's too far gone. After his death, the group mourns Alfie's loss. However, none of them have a clue what to do with his body. None of the dogs know what dogs do to their dead. Lucky wants to leave him as is and let nature take its course, but the former Leashed Dog feel it wrong to just leave him out in the open. They decide to emulate humans and bury him. Lucky finally agrees when Bella notes that Alfie would have wanted to be buried, just like his owner would have done. They say their last goodbye's to the sprightly Bulldog and guard over his body until the next morning.
The Leashed Pack makes its way back to their old camp. There's no drinkable water so they make an offering to the River-Dog for cleaner water. They give up a stick under the logic that most dogs like playing fetch (though Lucky finds this to be an awfully Leashed Dog idea). That evening a storm strikes. Most of the dogs start running around in fear of the thunder and, to make matters worse, the river floods. The storm doesn't bring only chaos as it leads to the pack discovering a series of caves. The water is also clean, or so it initially seems. Bruno starts choking after drinking some river water and is narrowly saved by Lucky.
Bella realizes this territory is not safe for their pack. They need a better territory, but the Wild Pack won't share. This is when she tell her brother of an idea she's come up with: Lucky will act as a double-agent and join the Wild Pack. Once he's gained their trust, he'll vouch for the Leashed Pack. Lucky reluctantly agrees to do this.
Lucky is let into the pack thanks to Sweet. Lucky is made a patrol dog and taught the in's and out's of the Wild Pack. He becomes used to his life amongst the Wild Pack and quickly begins to genuinely enjoy it. This is bad because he's not supposed to bond with these dogs; he should remain loyal to Bella and the Leashed Pack. He continues this double-life of reporting back to Bella while living as a Wild Pack dog for a while.
To get ahead in the pack quickly, Lucky challenges Snap. The two fight but Lucky wins due to his size advantage. Snap is demoted a rank, Lucky is promoted to a hunter, and Mulch is demoted so that Lucky can take his spot. This doesn't help the animosity Mulch has for Lucky.
Lucky tries to go and see his old packmates, but time and time again he is declined. First it's that Bruno and Martha need to heal, next it's that an illness has spread and it's best if he stay away for now. Lucky comes to the conclusion that maybe they just prefer him gone.
During one of these meetings, Lucky runs into Omega. It turns out that the slimy dog had spyed on Lucky and knew his secret. He promises not to tell Alpha if Lucky will make it so that he is promoted. Lucky decides to frame Mulch because of Mulch's past reputation as a food-stealer. He makes it seem as if Mulch ate before everyone else. Mulch is attacked and demoted all the way to Omega. The previous Omega, now referred to as Whine, is made into a patrol dog.
Some time afterwards, the camp is attacked while Lucky is away hunting. The attackers are a group of gray foxes and the Leashed Pack. It turns out they were planning this attack behind Lucky's back the entire time. The attack goes badly when the foxes double-cross the Leashed Pack. They head for Moon's den and try to take her pups. The two packs try to save the litter but one of the pups is killed, as is Mulch.
The book ends with the Leashed Pack apologizing and giving their side of the story. They simply wanted to share the territory, not lead to any deaths. Whine decide this is the perfect time to break his oath to Lucky and rat him out. Now everyone knows about Lucky's betrayal.
This book provides examples of:
- Animal Gender-Bender: A deer buck is referred to as female.
- Automobiles Are Alien: The dogs come across construction trucks and helicopters. Both are foreign and intimidating to them. The Wild Pack isn't even used to cars (with most members being raised away from the city).
- Becoming the Mask: Lucky finds himself growing attached to the Wild Pack, making his eventual betrayal harder. He's stuck between loyalty to his sister and loyalty to his new pack.
- Blackmail: Whine blackmails Lucky into framing Mulch.
- Cool, Clear Water: Subverted when the dogs go swimming in the river. It looks like the poison is gone until Bruno starts puking and foaming from the mouth a few moments after drinking some water. He's only saved by Lucky knowing how to head-butt a dog so that they'll vomit.
- Death of a Child: Fuzz is killed by foxes.
- Ear Ache: This is how Lucky wins against Snap. She's a small, quick-footed dog but she unfortunately has one disadvantage: her long, floppy ears. Lucky bites her ear and attacks the injury until she begs for mercy.
- Early Installment Weirdness: Lucky treats burial as unusual for dogs. He believes that dogs naturally let dogs waste away where they die and that burial is something only longpaws do. In future books, "giving dogs to the Earth-Dog" is established as a normal part of their Animal Religion.
- Fantastic Racism: Sweet and most of the other Wild Dogs look down upon Leashed Dogs.
- Fear of Thunder: The Leashed Dogs have no experience with being outside during thunder storms. They freak out and almost get themselves killed.
- Gonk: Omega is considered ugly to other dogs. His eyes bulge and his muzzle is too squashed.
- Half-Identical Twins: Spring and Twitch look a lot alike. The only differences are their sexes and Twitch's lame paw.
- Heroic Sacrifice: Mulch is killed trying to protect Moon's pups.
- The Load: Whine was an Omega specifically because of this. Pugs aren't just meant to live in forests. He's a terrible patrol dog.
- Meaningful Rename: Nuzzle became the Nature Spirit Wildfire when she grew up.
- A Minor Kidroduction: The prologue has Yap and Squeak's mother telling them about wolves.
- Mistaken for Romance: Despite Lucky's misgivings, Sweet is not Alpha's mate.
- Naïve Newcomer: Being a Lone Dog from the city, Lucky has to be taught the Fantastic Caste System of a proper pack upon joining the Wild Pack.
- No-Holds-Barred Beatdown: For seemingly having eaten before Alpha, Mulch gets beaten up by Alpha and Sweet.
- The Oathbreaker: Whine doesn't keep his promise to Lucky. He tells Alpha and the others that Lucky was a spy, all while ignoring the part where he got Lucky to frame Mulch.
- Punctuated! For! Emphasis!: Upon noticing the deer has been partially eaten already, Alpha says "Who. Has. Done. This?"
- Sacrificial Lamb: The youthful Alfie gets mortally wounded in the first chapter just to show how threatening Alpha is.
- Savage Wolves: Yap's mother describes wolves as craftier, wilder relatives of dogs. They're not to be trusted and should be kept at a distance.
- Took a Level in Jerkass: Gone is the nervous, shy Sweet from the last book. She's now the serious, not-to-be-messed-with Number Two of the Wild Pack. The contrast is so huge that Lucky doesn't even recognize her until they talk one-on-one.
- Wolves Always Howl at the Moon: The Great Howl is a spiritual thing that the Wild Pack does every night. It helps strengthen the pack's bond and is an enthralling experience.