Jim Pascoe 
Undertown #1 [EPUB ebook] 

Meet Sama, a 10-year-old boy who is so sad that tears have literally stained his cheeks. Sama’s father has had a heart attack, and doctors give him a month to live. With his teddy bear in tow, Sama crawls under his bed and finds a magical portal to a strange realm called Undertown. What is this dark new world? To find out, Sama begins a journey through the depths of Undertown, where he searches for The Sugar Stone, a magical object that might be able to save his dad!