In a small area of habitable land and low waters, most Selkies and landlings live in peace, though they do have their differences. The Selkies live in underwater buildings and can breathe air as well as water. Teen Selkies, such as main character Emily, hang out at Freddy Fish's and want to grow up to be amphibian musicians and dancers.

Some landlings despise the Selkies as much as Earth's Holy Warriors hate them. Possibly nobody hates them more than Chris Keating, who wants to help the religious Earth Avatar "Purify" the human race, embracing all who possess the Holy Human Genome into the Body Purified and killing all Selkies.

Keating hikes into the wilderness, where he finds and activates the Emergency Interstellar Null-Brane Beacon that was on Victor's spaceship. The Beacon transmits a distress signal that Keating hopes will be picked up by Earth, prompting the Holy Warriors to find Marseguro and destroy the fish-people.

On Earth, Richard Hansen notices the signal and is sent to destroy the Selkies. But Richard turns out to be a clone of Victor Hansen. At a time preselected by the deceased Victor, Richard's mind will fade and be replaced by Victor's mind. Richard will be Victor.

The Holy Warriors bomb Marseguro and massacre a huge number of Selkies, including Emily's best friend. It seems all might be lost for the peace-loving Selkies. But from beyond the grave, Victor has helped to create a biological weapon, and the Selkies intend to use it and eradicate the invaders from Earth.

Sounds like a 1950s flick, right?

Readers might think that Marseguro is like the old movies that pit blobs and fish-demons against humans. But Marseguro reaches far beyond the stuff from which our genre came.

For one thing, the humans are the attackers, and what they are attacking is an evolved human form created by one of their own. Think of the Avatar and Holy Warriors as Nazis or Crusaders; think of the Selkies as any persecuted religious or ethnic group in history.

The settings are well drawn and creative. The reader can easily visualize the underwater habitats and tunnels of Marseguro, the deep sea vacation homes and the strange restaurants that cater both to both humans and fish-people.

The characters possess substance, emotions and realistic motivations. Emily is clearly the heroine, a young girl seeking revenge on those who have attacked her world and killed her friends. Richard Hansen comes across as an extremely sympathetic character, one who hasn't evolved in this book quite as much as he could. Chris Keating is a misguided fanatic, the type of person we find in reality far too often.

Most important, the action and surprises keep coming. Willett sets his scenes, establishes the Selkies as loving, intelligent, almost cute creatures, and then lets loose with nonstop action and plot development.

The book ends with some unanswered questions, such as: Why did Victor Hansen create a modified human that breathes underwater as well as on land? The Selkies are unusually strong, but why wouldn't Hansen make them into full intellectual and physical super-beings? Why would the Selkies leave the Beacon in the woods, ready to be used at any time? After all, they fled Earth and went into hiding, so why leave a device that signals Earth as to their whereabouts? How can Victor's memories and knowledge suddenly be triggered to life in Richard's brain?

Overall, however, the flaws are minor, and this book is almost impossible to put down.