Earlier this week I put the finishing touches to the fifth and final Furnace book. It was a weird experience, one which came with a bittersweet mix of emotions. On the one hand it was amazing to bring the saga to a close, to see Alex and his friends get to the end of their journey. And it's been a hell of a journey, quite literally in some cases!

It was a huge relief to make it to, and through, the last few chapters, especially as I had no idea, really, about what was going to happen. I said from the start, from the very first word of the very first book, that I wasn't going to plan these stories – I wanted to experience them from exactly the same place as Alex, not knowing what was going on or why. That way his actions and his thoughts would appear more realistic, more genuine. Of course there was always the danger that I'd get to the final book and not know what was happening, or why, and that was a big worry. But the story just seemed to know where it wanted to go, and it went there of its own accord and under its own steam. I just wrote it all down! It really was an amazing feeling being able to wrap up the series in a way that makes sense, and which hopefully leaves everyone satisfied.

But along with the joy of finishing the series comes sadness too – grief, almost. Because it means saying goodbye. I'm not going to say who makes it to the end alive, you'll have to read it yourselves to find out! But even the ones who survive have to say farewell. This is the end of their adventure, and even though in my head they'll be going off to live the rest of their lives I will no longer be part of it. It may seem like a weird thing to think, but I'm not lying when I say that I'm closer to Alex and Zee and Simon and Donovan than I am pretty much any of my actual friends! For the last three years we've been through so much together, and for the last six weeks especially it's been an incredibly close bond made even more intense by the fact that we all knew this was our final journey together. Writing those last few pages was so good because it was the end, but it was so sad too because it really did feel like I was losing my friends.

It was pretty much exactly three years ago, in July 2007, that I started writing the first Furnace book, Lockdown. It feels like a lifetime! Three years, 375,000 words, and a story that is far from perfect but which I'm pretty proud of. I don't really want to let it go. I'll drop in on Alex and the others every now and again. They live in that weird place in a writer's brain, a home for old characters. They'll be there with Nate and Cat and Clint from The Inventors, so they'll be in good company! And you never know what might happen in the future...

But for now, I just want to say a huge thank you to Alex Sawyer, Zee Hatcher, Simon Royo-Flores, Carl Donovan and everybody else who was inside Furnace with us. You've made the last three years some of the best in my life!