It is a very elegant game from the days before electronic games were much more sophisticated than "Pong". You can have a closer look at it on Boardgame Geek.
Reading is a solitary activity. No one is going to want to wait around twiddling their thumbs while the person they're playing with silently reads a few pages, maybe tosses some dice, reads some more, then maybe finally does something that affects their game. Neither of those concept killing ideas occurred to me, or if they did, I brushed them aside. But I did realise that it would be a lot of work to pull off, after all a two player book system would need... two books, at least, and maybe a bit more. I'd already written three, and they had taken me quite a bit of time and effort to put together. Plus this one would require the invention of some two-player mechanism.
So I looked around for some assistance and decided to ask my friend Martin Allen to write the thing with me, though this would be his first game book project. We developed the concept of a competition between brothers for a throne and decided to split the work down the middle with each of us taking on one book. Martin would take on The Warrior's Way and I would tackle The Warlock's Way. It was our plan all along to make the books able to stand alone, with the two-player element added as a sort of bonus feature for those that wanted to use it. We always envisaged the books being released separately.
Since the books would have to stand alone (so we thought), the single player part of each volume would have to be as long as a standard game book: 400 "paragraphs". We settled on tacking on another 100 paragraphs to each book to accommodate the shared sections. Thus we were looking at 1000 paragraphs, or two and a half books. Warning bells should have been sounding in my head at this point. This was a lot of work to be throwing at something that we had no real idea was a good idea (it wasn't), and for an idea that had been greeted by Penguin without enthusiasm.
Writing it was agonisingly slow, and there were many uncertainties about developing the two-player elements. I'm certain that it was a much longer and more tortuous process than would have been required to write two and a half "regular" game books. Yet finally it was finished and sent to Penguin, where it disappeared into a cloud of disinterest. No doubt the publisher's good sense told them that this was a stupid idea that would never fly.
Many months went by. Penguin could neither bring themselves to go ahead with the project, nor reject it. Yet finally there was movement. Some other publisher was going to bring out their own two-player game book! I think this may have been Mark Smith's and Jaimie Thomson's Duel Master series, but I'm not sure. In any event, it put a firecracker under Penguin's arse (or at least the cheek devoted to Fighting Fantasy). Suddenly they wanted Clash of the Princes and they wanted it NOW. Finally some editorial work went into it, pushed along by this sudden sense of urgency, and much anxiety on the Puffin editorial team's side that the two-player mechanism might not work.