Maskmaker - Jane Johnson

When Jamie's mysterious art teacher sends him to the old Maskmaker's
shop, he is faced with a terrible decision. He must choose a
disguise that will take him into mortal danger, with only a talking
cat to help him. In the deserts of Africa, the frozen glaciers
of Greenland, and the Great Wall of China, Jamie will need all
his intelligence and courage if he is to save his friends and family.
Will the perilous tasks he faces help him solve the strange problems
in his own life? Or will a dark web of sorcery stop him from
ever coming home again?
"Extremely well written, highly inventive and with really funny jokes."
Eva Ibbotson