When Humans nearly destroyed themselves with catastrophic climate change and the resulting wars, they were contacted by the seven-billion-year-old galactic federation known as Concord. The aliens granted Humans probationary membership in Concord and helped us begin to reverse the damage done by centuries of neglect. Select individuals were allowed to serve as crew on Concord spaceships. Five hundred years later, Emma Fuji is the sole Human among a million aliens aboard a spaceship the size of Pluto called Violet Enforcer. Her official job is to introduce Humans to the other Tribes of Concord, through interviews and personal encounters. She succeeds in large part because her pet terrier, Moondog, becomes a superstar celebrity among the aliens, who have never seen a pet before-let alone a feisty, gray-and-white pup who won't stop climbing on aliens and begging for tummy rubs. When an unknown group begins sabotaging the surveillance drones in several systems, and Violet itself is nearly destroyed, the initial suspicion that Humans are responsible is dismissed out of hand: the sabotage technology is within Human capabilities but it's not quite like anything Humans ever used, and Humans have no reason to sabotage themselves. But a Human-crewed ship is vaporized by the same tech, and a group of fanatics on Earth who have renounced any dealings with Concord claims responsibility. Humans are once again under suspicion. The goal of the Renouncers is to convince humanity to withdraw from Concord, and if they are truly responsible they'll get their wish. Unfortunately, history shows that Tribes that resign or are banished from Concord don't last long. If Humans have actually been sabotaging Concord, and are responsible for the tens of thousands dead so far, it will mean the end of the Human race. As the number of sabotaged systems continues to climb, Emma and her closest alien friends race to prove that Humans are blameless. Ranging across an entire quadrant of the Milky Way, from the globular cluster where all the AIs ever created have retreated to a scoured neutron star, to the planet being terraformed to be a second Human homeworld, to Earth itself to interrogate the Renouncers, Emma and her team search for clues to the true identity of the saboteurs. In the end Emma's strength, intelligence, and compassion are nearly enough to solve the problem. But the final evidence is revealed by the charm and instincts of the galaxy's most famous canine, Moondog.