Investing your time in a book series is a risky proposition. We only have so much time to read, so we obviously want the books we choose to warrant the time spent. Bookshelves everywhere are littered with series that started out strong only to peter out due to creative stagnation, diminishing returns or George R.R. Martin-esque gaps of time between installments. As one might imagine, a series that manages to largely avoid all of those pitfalls is something special indeed.

Charles Stross has given us just such a series.

Stross has just published the eighth book in his cleverly, creepily compelling Laundry Files series, titled “The Delirium Brief” (Tor.com; $25.99). It continues the story of Bob Howard, employee of Britain’s supersecret occult spy agency devoted to protecting not just the country, but the very fabric of our reality.

And it hasn’t been going so great.

The last book saw much of Yorkshire destroyed by an invading extradimensional force of, well … elves. While Bob and his Laundry cohorts managed to ultimately defeat the enemy and thwart the invasion, the scope of the incursion meant that the supersecret Laundry was no longer supersecret. The revelation of the existence of an occult defense agency – not to mention the destruction caused by the onslaught of the Host of Air and Darkness – has unsurprisingly led to a lot of questions.

So Bob, who is still adjusting to his newfound status as the Eater of Souls (don’t ask) and dealing with some marital strife with his (newly-promoted herself) wife Mo, has become the erstwhile face of the Laundry, going on news chat shows and in front of government committees to answer those questions as best he can while still attempting to maintain the integrity of the organization.

However, there are dark forces afoot that see this turmoil as an opportunity. A sinister figure from Bob’s past – someone that he believed to be gone forever – has returned, armed with a legion of fanatically devoted followers, massive amounts of cash and weapons both conventional and magical. The fate of the Laundry hangs in the balance – as does that of the world as we know it.

Pretty typical stuff for Bob, really. All he has to do is stop the bad guy, save reality and figure out how to fix his marriage and avoid consuming too many souls. Oh, and maybe overthrow the British government. No big deal.

The Laundry Files novels have experienced as clean an evolution as any genre series you’re likely to find. The early books had Bob as a bumbler, someone who stumbled through a world that he only barely understood in a fog of confused, self-deprecating humor. But as his adventures continued, he logically became more adept and accomplished – though Stross did well in continuing to keep him out of his depth.

Some of the subsequent books spent time with other main characters, giving the reader a chance to gain new and different perspectives on the Laundry – as well as maintain the in-over-their-head vibe that made those early books so much fun.

Now, with “The Delirium Brief,” we have a Bob who, despite being endowed with unbelievable power, is still in many ways the guy we met all the way back at the beginning, a good-hearted gentle soul who still can’t believe that he’s got to deal with gibbering tentacle monstrosities from beyond the dimensional veil.

Maintaining the joyful blend of humor and horror throughout the series can’t have been easy, but Stross has managed. The interpersonal relationships have grown and the supporting characters have been thoroughly developed; long-dangling threads have been revisited, retied and – in some cases – resolved over this eight-book span.

“The Delirium Brief” is typical Stross and typical Laundry Files. It is smart and funny and weird and scary, driven by engaging, endearing characters and a vividly-detailed world that has been built with exquisite care. To maintain a level of quality this high for this long is a remarkable feat; frankly, I envy those readers out there who have the opportunity to read this series from the beginning for the first time.