After a long covid pause I visited my parents' house. I took some things back with me, such as this:
This is a choose your own adventure book that originally belonged to my big sister. For those who don't speak Finnish, the book is called The Haunted Railway Book and it uses the characters from Enid Blyton's Famous Five, which is a well known series of adventure books for children (or maybe YA, don't know, I haven't actually read any of them).
The game itself is fairly involved. Instead of just doing random choices you have multiple items like a map and a compass that you can obtain and lose during the game and even hit points that are visualised as, obviously, food. I figured it might be interesting to work out how the game has been designed. Like all adventure game books the story has been split into different numbered chapters and you progress in the story by going from one chapter to another according to the rules.
In other words the game is a directed acyclic graph. Going through the entire book and writing it out as a Graphviz file, this is what the adventure looks like. The start point is at the top and to win you need to get to the second to last node without losing all your hit points and having the code book in your possession. The gv file is available in this repo for those who want to examine it themselves.
The red nodes are those where you lose one hit point. As you can tell the game really does not go easy on the player. The basic game design principle is simple. At first the decision tree fans out to give a sense of freedom and then chokes back down to a single node or few where important plot points are presented. This pattern then repeats until the story ends. In this way the game designers know that no matter how the player gets to the endgame, they have been told certain facts. Given that this book was designed in the late 70s or early 80s when computers were not that easily accessible this approach makes designing the game a lot easier as each story segment is fully isolated from all others.
Looking closer we can see how the hit point mechanism works.
This is a repeating pattern. The game checks if you have a given item. If you don't have it you lose one hit point. In either case the plot goes on to the same point. Note how the child nodes have very different numbers. One assumes that if they were consecutive the player might read both branches and feel cheated that the event had no real influence on the story.
One thing that I wanted to find out was whether the game had any bugs or shortcuts you could take. There do not seem to be any. When I first wrote the graph down there was indeed one path that jumped past several plot nodes. I verified that it was not a transcription error and it did not seem to be. So either the original game had a bug or the Finnish translation had a typo.
Then I re-verified the transcription and found the issue.
In this chapter you need to use a code book to decipher a secret message, which seems to be the letters EJR that translate to "go to chapter 100". However the black triangly thing that is completely separate from the rest of the text (helpful arrow added by me) is actually part of the message and changes the content to "go to chapter 110". With this fixed the transition no longer jumps over plot nodes. (The chapter text does say that the message is split over two separate bricks, but who reads instructions anyway.)
So what can we learn from this? Graphic design is important and too much whitespace can lead to smugglers escaping the long arm of the law and the short arm of child detectives.