Castle MacPelican is the home of Hector MacPelican, inventor of extraordinary machines and Head of the Clan MacPelican. When Thomas and Esmerelda arrive there for a visit, they find that Uncle Hector has set them each a treasure hunt, with lots of puzzles to solve and things to spot along the way. The setting of each highly-detailed double-page spread is a different room in the castle. As well as joining in the treasure hunt, the reader has, in every picture, to help the spiders Spinner and Webley find a route to escape from Dustina, the maid; find all twenty MacPelican dogs; help Aunt Forgetlia recover the things she has lost; discover if Great Uncle Figment is telling the truth; assist Snoddy the Butler in tidying the castle; spot the thief and find what it is he's stolen - and lots more besides! Scoular Anderson spent a number of years working as an illustrator for London University. He turned freelance in 1986 and has illustrated over a hundred books - around thirty of which he has written as well. These include many joke and puzzle books, picture books and non-fiction. He has also written a play and a number of stories for adults that have been broadcast on BBC Radio.

While on a field trip to the museum to learn about ancient Egypt, Mrs. Pudget's class searches for hidden objects and solves puzzles in order to return to the present.

Because they take all the wrong turns and have other major problems while traveling to the Grand Louisiana Exhibition in 1898, the MacPelican clan needs the reader's help to find the way.