The Dark Secret of Weatherend — John Bellairs

From his adventures in The Treasure of Alpheus Winterborn teenager Anthony Monday returns to take on a storm of sorcery.
 
Anthony can always count on his friend, sixty-eight-year-old librarian Miss Eells, to break up Hoosac's hot summer days with some adventure or other, but this one takes the cake. On their way to get ice cream, they make a side trip to the abandoned mansion of the late J. K. Borkman, a once rich and weird eccentric who was obsessed with the weather.
 
When Anthony finds a diary there, the pages seemed filled with the ramblings of a crazy old man, until Borkman's son starts fixing up the dilapidated house -- and the storms come. Hail, lightning, and dangerous winds descend upon Hoosac. And when Anthony and Miss Eells connect the wild weather to the diary, they uncover a diabolical plan, black magic, and a son more than willing to finish what his father started . . .
 
“A wild, ghoulish plot . . . There's a nice balance most of the way through between folksy charm and gently intense suspense.” -- Kirkus Reviews
 
“The atmosphere Bellairs creates is creepy and a little chilling . . . So, wait for a dark and stormy night, grab a blanket and a flashlight and enjoy this eerie mystery.” -- SF Site
 
“Fast, witty and intricate entertainment.” -- Publishers Weekly
 
“Pure Bellairs.” -- School Library Journal