The Lion, the Witch and the Wardrobe (1950) and was originally published first in the chronicle of Narnia series.
Published also by Scholastic.
Also packaged as part of a seven book boxed set.
NOTE
Accelerated Reader MG 5.7 6 52
Summary
Four English schoolchildren find their way through the back of a wardrobe into the magic land of Narnia and assist Aslan, the golden lion, to triumph over the White Witch, who has cursed the land with eternal winter.