A book by John Bellairs
that involves a plot
to take control of the earth
by changing the movements of the Oort Cloud
of comets. The scheme is undertaken by an evil
scientist/professor type who has stolen a set of carved ivory chess
pieces from the British Museum
which are being used in a sinister magic ritual. The chess pieces were supposedly Viking
artifacts uncovered on one of the islands in the Outer Hebrides
The protagonists of the story are Bellairs' usuals: Professor Childermass, Johnny, and his friend Fergie.
In the British Museum, there is in fact a set of ivory chess pieces from the Outer Hebrides, which undoubtedly inspired the story.
I read every John Bellairs book as a child (which instilled in me a lifelong passion for Edward Gorey) but this was undoubtedly my favorite, although it's been so long since I read any of them that I can't quite remember why... (There was also another excellent one where the Professor and Johnny go back in time to Constantinople using a refurbished subway but I can't remember the title (if YOU do, please /msg me!)). On a family vacation to London when I was seven, I was considerably more excited to see the chessmen than the Rosetta Stone.