The Argonos is a huge starship travelling from star system to star system. It hasn't made land in 14 years and the crew are getting restless. When they receive a signal from a planet they name Antioch, a team is sent down to investigate. This may be a chance to change the fortunes of the wandering ship. Mutiny is brewing, not just potentially from the divisions controlling the ship, but also from the service crew. On the planet they come upon a gruesome scene which leads them on to the discovery of an alien vessel - the first evidence of an alien civilisation that they have ever come across.
The background of the Argonos and the history of why they are travelling is shrouded in mystery and vagueness. Either Russo is just too lazy or disinterested in creating a setting or just doesn't have the technical background. Conveniently obscuring the deficiencies in the plot and the writing, all background into the ship's history has been lost after the Repudiation - a plague that destroyed a third of the ship and all of their logs 273 years ago. But get this - the Church has secret archives! So they investigate these to see if they can find anything useful and what do they find? Nothing. "Uh, captain, something blew-up. We don't know what caused it", is about the depth of technical information we get here. This is definitely not hard-sf.
This wouldn't matter so much if the author delivered on the potentially interesting premise of the book, working on a pure story-telling level without getting bogged down in technical details or the envisioning of imaginary worlds - but it doesn't even manage that. After a great deal of padding and false, pointless trails, Unto Leviathan descends into Alien-movie territory and finishes with an anti-climatic and open-ended finale. Very disappointing.