Its so beautiful…

They are Jake Bloodworthy, a Spell Master Apprentice, and Maribelle Cringemine, a Wizard whose family controls the dark forces in the kingdom of Hogkym.
He needs Wizard blood to prevent himself from falling under the influence of the dark force's magic.
They are in a desert because they must travel across Hogkym to defeat the Darkhog, Lord of the Dark Forces, at his Palace which is at the end of the desert.
She sacrificed her own arm to perform a spell which would prevent her from ever dying of blood loss so she can continue to provide blood for her non-Wizard lover.

Anymore questions?