Lewis is a newly orphaned, plump ten-year-old, who wears "purple corduroy trousers, the kind that go 'whip-whip' when you walk." The author often claimed that his imagination got stuck at ten, and here is Lewis, age ten, going to live with his Uncle Jonathan in New Zebedee, Michigan. The year is 1948, and New Zebedee bears a strong resemblance to Marshall, Michigan, where the author was born -- The Cronin House and the GAR (Grand Army of the Republic) Hall still stand in Marshall, just as their counterparts do in New Zebedee.
The House with a Clock in its Walls is a whimsical horror tale involving a deceased wizard's scheme to end the world. The book was illustrated by Edward Gorey (speaking of whimsical horror), and was at one time transformed into a made-for-tv movie for children.
So far from what I've read of Bellairs, his characters tend to be elderly eccentrics, or ordinary children (no superkids, here). Lewis is resourceful, but with a child's fears and limitations. Most especially, he is afraid that his uncle won't like him, that the kids in his new school will make fun of him, and that he'll never have a friend. His uncle Jonathan and neighbor, Mrs. Zimmerman are skilled in magic, and are very likeable. They perform magic tricks for Lewis and make him chocolate chip cookies and coca, and generally treat him as a small adult. The one thing Uncle Jonathan is reluctant to talk about is the ticking noise within his old house.
Lewis discovers that his uncle makes midnight excursions throughout the house, stopping and restarting all of the old clocks. He slowly gets involved in the mystery of the undiscovered clock. The wizardly Izzard couple who used to live in the house are both dead, but what did they leave behind and why?
There are some genuinely frightening scenes in The House with a Clock in its Walls -- most especially when Lewis tries to impress a new friend by stealing one of his uncle's magic books and taking it to the graveyard at midnight on Halloween -- but I don't want to spoil the story for you (Hint: there's a scene straight out of "Count Magnus" by M.R. James when the lock pops off of the crypt). Let me say that this is a truly scary book, and if the author's imagination got stuck at ten, he must lived an awesomely spooky tenth year.