The reviewer of a sequel has a challenge not unlike the author of the sequel. The reviewer needs to write up a review that doesn't sound like he's merely parroting his review of the previous book, while the book's author tries to make the sequel as compelling as the first book without essentially copying it with minor changes.
Liars and Thieves is not simply a rewrite of Fathers and Sons, although there are similarities between the 2 books (which is natural with any book series). The main characters of Filagroo (e.g. Pleebo, Roustaf, Nestor, Walcott) reappear, trying to fight the good fight against the warmongering Ochans. The super-powered teenagers of Earth are also in the spotlight again (Tommy, Staci, Owen, Nicki, and Donald).
The back cover of the book mentions that the stakes have been raised - and that's certainly the case. At the start of the book, Roustaf needs to recruit the five youngsters on a rescue mission to save Pleebo and Walcott. However, since this time they are each allowed to make a deliberate choice, not all of the kids immediately agree to travel back to Filagroo.
Though the book introduces several new characters along the way, it doesn't add too many of them so as to be overwhelming. Also, each of these new characters is both interesting and necessary (i.e. none of them are "Jar Jar Binks" types). One of the saddest scenes, for me, was the one where Captain Fluufytail (yes, with 2 "u"s) is adrift at sea, his ship having been reduced to just ash and splinters by the brutal Ochan assault. One of the most fascinating characters introduced was Krystoph - a former Ochan general who has come to side with the Filagroo rebels against his former king.
In a blurring of the lines which seems harsher than in the previous book, Krystoph is written as being - to some degree - sympathetic and his (mostly submerged) good side seems to come out when the occasion calls for it (e.g. when he saves Staci from being trampled to death). At the same time, the reader is shown quite clearly what a merciless killer he has been - and still is. Tommy, who seemed to have a bit of a dark side in the first book, is seen to have an even darker side - one which either was subdued before or has developed since his last adventure. Christopher Jarvis, who in the first book is seen as little more than a pathetic abusive father, is shown to have a heroic nature in this book.
Whereas, in the first book, Tommy and the super-youths were seen to be mere vessels for a power they couldn't control, in this book they are shown to be in greater control - and to be enjoying using their power, even if it causes others to be harmed or killed.
As with the first book, there are flashback scenes which help provide context for the scenes in the present.
Though the first book had a definitive ending - a victory for the heroes, the return of the youngsters to their home planet, Zanell's acceptance of her new role among her people - this second book does not and leaves the reader a bit unsatisfied (as The Empire Strikes Back did with Han's final fate unknown). By the end of the final chapter, the Ochans seem to be winning the war, two of the youngsters are in prison, Tommy may be reunited with his dead mother (or is just hallucinating) and Pleebo is trying to escape being recaptured.
Although there is little mention of Tommy's artistic abilities in this book, I wouldn't be surprised if it becomes a major plot device in the final book. I also think that it's not a coincidence that the series has 2 characters named "Chris" (Christopher Jarvis and General Krystoph). I'm certain the literal or symbolic link between these characters will be made clearer in the next book.
I would recommend this book for the young adult fantasy collections of public libraries (especially if the library has already purchased Fathers and Sons and intends to buy the final book of the trilogy).