Original: Aang and his friends discover that an upcoming solar eclipse will deprive Firebenders of their bending , leaving them open to invasion and giving Aang his chance to defeat the Fire Lord , but in learning this Aang 's Sky Bison is lost to a group of Sandbenders .
Simplified: Aang and his friends discover that an upcoming solar eclipse will deprive Firebenders of their bending , leaving them open to invasion and giving Aang his chance to defeat the Fire Lord .