In the catastrophe called the Waste, all polar ice melted, the seas rose 300 feet, and wars, famine and plague killed 90% of all humans and half the other species on Earth. As we stood on the brink of extinction in the early 22nd century, the galactic federation known as Concord contacted us and asked politely if we really meant to do that. When we asked for help, we were invited to join Concord as a probationary member, and the aliens immediately began helping us back to our feet.
Concord consists of 44 Tribes (including us). It monitors every star and planet in the galaxy and keeps the peace. Sixty other living Tribes declined membership, and are protected by Concord but not allowed to leave their home systems. Most of these Hermits only last a few million years before fading away. Concord was founded by two tribes seven billion years ago, one of which, the Pilots, are the only Tribe that knows how to navigate faster-than-light spaceships.
Five centuries after humans joined, an unprecedented series of sabotages begins, starting with the enormous warship Violet Enforcer. The sole human aboard this ship of one million people is Emma Fuji, the daughter of a Scottish doctor and a Japanese relief worker. Emma is tricked into going outside the ship with a faulty suit, and only quick thinking, meditation, and luck save her life. The investigation that follows also turns up a time-delay bomb that would have obliterated the ship.
Emma's official job is to introduce humanity to the six other Tribes that have habitats on Violet Enforcer. She does this in regular live interviews with her mentor, a five-limbed, three-faced, feathered alien who has a well-developed sense of humor. The interviews are a hit on the ship's network, but shortly after the sabotage begins, her star is eclipsed when her terrier, Moondog, becomes the bigger celebrity. Everyone knows Emma, but everyone loves Moondog.
When the immediate crisis is past, Violet begins investigating other acts of sabotage in several solar systems. There are hints that humans may be responsible somehow. Then another ship, the only ship with a human crew, is destroyed by the same kind of bomb that was placed on Violet, and a group of human radicals that want humanity out of Concord claims credit. Violet travels first to Earth to investigate these claims, and then to the planet that Concord is terraforming for us when we leave probation. More and more evidence piles up that humans may be at fault, but no one wants to believe it. If it's true, humans would be confined to Earth, and the chances of us surviving even a century after that are slim.
In the end, Emma and her friends discover the bitter truth and deliver justice -- but not without the help of Moondog, the most popular dog in the Universe.