The Xanadu Adventure, published a full 15 years after the somewhat open-ended "Philadalphia Adventure," attempts to put a definitive end to the adventures of Vesper Holly. In retrospect, the plot is solid traditional Holly fare. The execution, however, is severely lacking.
Unfortunately, simply too much time has passed between the writing of the last book and this one. At one point in Xanadu, the characters remark how an author can lose his inspiration. The same seems to have happened with Mr. Alexander in this book. More specifically, he seems to have lost a grasp of the characters and what made the series tick in the first place. If his name wasn't on it, I'd swear it was written by a different author.
As I said, the plot is solid, and there are times when the dialogue is pure Vesper Holly classic. Unfortunately, there are some serious problems with the characters overall that are just impossible to overlook. Often Alexander has them saying lines that are basically making them caricatures of themselves. Vesper, for example, repeatedly refers to Brinnie as her "dear old tiger," which is a reference to a few lines in the first book of the series, but instead of invoking a clever tie-in, just comes across as hoakey and false.
The voice of the novels, "Brinnie," is the biggest disappointment. His character comes across as ignorant and silly at times instead of the steadfast, loyal companion to Vesper he has been in the past. For example, at one ridiculous moment, he threatens to cut someone's mustache down to its roots with a butter knife. Lines like this would never had existed in the original series.
Also lacking are the clever observations by Brinnie that made the original books so witty. All we ever get are his thoughts on how to handle situations, instead of getting actual analysis on how others are behaving. He seems -- I don't know, self-absorbed, in a way. Even then, he's the only character who really comes across as three-dimensional. Even Vesper, supposedly the star, seems relegated to some sort of ensemble cast, and therein is the book's biggest problem: Alexander forgets in this book that when it comes right down to it, the Vesper Holly series is not an ensemble, it's an adventure series whose highest points come in the relationship between Vesper and Brinnie. The two of them do not carry on a single conversation throughout the entire book without other characters nearby and the book loses its heart because of this.
And, of course, there's Helvitius, one of the greatest my favorite villain of all time. His character sadly degenerates here into some type of a sad imitation of its former self, where he's relegated to some moustache-twirling villain of silent movies. It's just a waste, really.
Also, unless you are a student of Greek mythology, the endless quoting and references to Trojan horses et al. is probably going to come across as a bit heavy-handed, far moreso than previous installments in the series.
One final thing -- the book ends with a very sweet, sentimental ending that should have, could have worked, but doesn't, because of the background to it. Essentially, Vesper marries the Weed two-thirds through the book in a whirlwind wedding that hardly gives room to breathe. It's simply out of character for the heroine -- not in the fact that she would get married, since I always assumed she would, but because in doing so she hardly even speaks at all of the affair to Brinnie, even knowing full well she'll be leaving him. Those who read the previous books know that, as free a heart as she has, the person who really occupied it was Brinnie, and the fact that the two never even converse about the fact that she is getting married just comes across as false.