And Another Thing..., By Eoin Colfer

Trilogies which extend to six volumes – not to mention continuations of deceased authors' profitable franchises by other hands – are a phenomenon endemic to the sort of rubbishy science fiction/fantasy Douglas Adams set out to skewer mercilessly when he began The Hitchhiker's Guide to the Galaxy as a radio serial in 1978. Yet, after numerous mutations from the first (and, frankly, best) iteration of the story, here is just such a shameless beast.

Adams was good at jokes, ideas and broad-strokes characters, but never mastered plotting, prose that didn't sound like instructions to the sound-effects department or learning when to leave well enough alone. Eoin Colfer has demonstrated in his own books for young adults all the novelistic skills Adams never managed to attain – but in this Hitchhiker's Guide "Part Six of Three", it takes him 100 pages or so to sort out the mess left in the sub-standard fifth book in the trilogy (Mostly Harmless). In that, the author – in one of those contradictory fits common to creators shackled to enormously successful series – slaughtered the entire regular cast and wiped out every possible Earth. And not in a funny way. Colfer plays fair, and doesn't quite pull an "all a dream" to save Arthur Dent, Ford Prefect and Trillian, the well-remembered leads, plus Arthur and Ford's less-well-remembered grumpy daughter, Random. However, he has to twist in the cosmic winds to get his own story going, which involves factions of continuing characters haring across the universe to a world where a mock-Irish entrepreneur has created a retreat for wealthy Earth people.

The planet-demolishing bureaucrat Vogons want to finish off Earth humans, though it's hard to get worked up about this since, Arthur aside, all the survivors of the planet are hard to care about. Colfer does Adams's characters well – though he clips trickster Zaphod Beeblebrox of one of his heads (revoking a one-off radio gag which has plagued every subsequent manifestation) and leaves the resurrection of the Eeyoreish Marvin the Paranoid Android (killed off by Adams two books back) for later.

The book has to walk a tricky path – diverge too much from Adams's tone, and it won't be embraced by the fans; simply rework old jokes, and it's hard to see the point. Colfer does bring new stuff to the table, especially in business with slightly sad Gods ranging from Lovecraft's Great Cthulhu to the Norse (well, Marvel Comics') Asgard, which seems more Pratchetty than Adamsian. He also gets the fundamental melancholy of the whole thing, where the bright-spark ideas and long strings of bizarre thought are all in the service of a vision of the universe as gently running down and stuffed full of self-important idiots, whining victims, insanely violent species and great extinctions.

After four episodes, Adams ran out of puff and John Lloyd had to come in and help him end the original story – a circumstance which has served to hobble many subsequent incarnations (the film, for instance, couldn't use Lloyd material and fizzled at the finish). There's a sense that more books will appear and, maybe now the decks are cleared, Colfer will have the opportunity to bring more to the mix.