The characters must get back to the mainland. This will provide an interesting little sea-voyage. When they reach land they are in a completely foreign country, and have significant language difficulties. Then, in customs, the Blue Book turns up and they are arrested for possession of a stolen artefact. Whilst in prison they are made to understand that they will be tried fairly, but in reality when their case comes up the language difference means that they do not understand either the charges or the verdict. Until the judge puts on his little black cap and they are roughly taken away and locked up. They're going to have to escape or be executed.
When they finally find a guidebook that lets them speak the language, they can find out the history of the Blue Books (for details of this extraordinary history, look at the entry of Blue Books in the Items database of this same website).
A potted summary of the history is that the books used to belong to an evil wizard who would use them for his own naughty purposes, but one of his apprentices stole one of them from him and went into hiding on his island. Now Alcylar Ahem Zed, the evil sorceror will be given the book back by the authorities who confiscated it from the characters.
If the characters wish to, they can now go and confront Zed in his Ziggurat-Maze.
The maze is a truly weird place, with many tricky puzzles. I will post some ideas for these puzzles on the Ideas database of this website.
It might prove interesting if you introduced another group of characters to the adventure at this point, sent into the maze by a rival wizard who wants to get his hands on the books for his own ends. A dual-GM system could be set up where the two parties compete to reach the end of the maze first.
If and when they get to the central tower and confront Zed, he will turn out to be a blue dragon.