Though they're packaged as Star Trek: The Next Generation books, the Double Helix series really spans all known Trek, featuring characters from all four series and an entire novel centered around New Frontier's Captain Calhoun. The good news is that this means there's something for everyone, with Spock and McCoy in the Unification period, Dukat and Kira during the Occupation, Tuvok in his Starfleet days, Chakotay, Torres and Tom Riker in their Maquis days, and just about everyone else in the current Trek universe popping in for a guest appearance.

The flip side, of course, is that certain characters are bound to appeal more to readers than others, so a six-book committment at $6.50 a book is pretty hefty. (The series was published in 1999, but I just managed to finish them.) It's possible to skip around or to read out of order, but the experience is much more powerful when reading all the books in order.

John Gregory Betancourt starts the series off very well with Infection, a first season TNG story about a mysterious plague, manufactured by an arrogant villain who leaves a clue encoded on a protein strand. The science is fascinating, and the TNG characters are well-drawn - particularly the late, lamented Tasha Yar, as well as Beverly Crusher - but it's a little disappointing to learn at the end that the crew was essentially being used as practice to test Starfleet's response skills while a brilliant enemy plots much broader destruction.

In the second novel, Vectors, Cardassians and Bajorans blame one another for an outbreak of the plague on Terok Nor while Dr. Katherine Pulaski works with Dukat to cure the illness before the Cardassian fleet mobilizes to kill everyone on the station - and on Bajor - to contain it. There's some marvelous Kira/Odo interaction and some backstory on Pulaski, though at times she seems to have changed personalities in the short time since her tenure on the Enterprise.

Diane Carey's Red Sector, the third novel, has a superbly engaging plot about a crisis in the Romulan ruling family, with a half-dozen original supporting figures who deserve to have more stories told about them. Yet the main characters don't quite sound like themselves - particularly Spock, although he didn't quite sound like himself in the "Unification" episodes either. The longest and heaviest of the series' novels, Red Sector will probably be the favorite of many readers, but it's also the book most easily skipped by TNG fans not nostalgic for McCoy's idiosyncracies or Spock's moving recollections of Kirk's command.

John Vornholt's Quarantine isn't as ambitious as the previous novel, but it's a fast read and a great deal of fun. One desperately wishes the commanding, ideologically focused Chakotay of this story on Star Trek Voyager, and Vornholt does a nice job with Torres and her Klingon temper as well. But the most engaging character is Tom Riker, who starts out sounding a lot like Will and ends up growing into a different man, in some ways a stronger man than Picard's second-in-command. The issues surrounding the DMZ are a bit undercomplicated, but the descriptions of the plague are effectively horrifying.

Peter David's Double or Nothing will probably appeal to New Frontier fans, but for people like me who haven't followed the series, it's a little much Calhoun. Of course it's nice to see Shelby, and this novel features Nechayev, Jellico and Sela as well, but I can't help feeling like Calhoun didn't deserve such a big role in resolving the situation. A subplot involving a sexy damsel in distress with whom Calhoun has mindless sex didn't improve matters any, except that it's more eroticism than most women are allowed in Trek. There's a decent amount of humor and a fairly interesting plot involving the entire Federation, but I'd have preferred one of the regulars working with Picard to stop the Double Helix virus.

The final novel in the series, Michael Jan Friedman and Christie Golden's The First Virtue, goes back before the first novel to explain the source of the vendetta which unleashed the deadly virus. The story focuses primarily on Jack Crusher and Tuvok hunting for a terrorist, while a young Picard - captain of the Stargazer - tries to keep the peace between aliens who blame one another. It's a shorter, simpler story, and the effect is sort of like reading C.S. Lewis' Narnia Chronicles in the order in which they were written - this is The Magician's Nephew following The Lion, The Witch, and the Wardrobe. I enjoyed it but it felt rather like a long afterword.