Complex sentence: Dr. Zachary Smith, a mole employed by the Global Sedition, reprograms the mission's robot to destroy the ship and crew, but is betrayed by his employers and left as an unwilling stowaway when the "Jupiter II" blasts off.
Split into simpler sentences: Dr. Zachary Smith, a spy employed by the Global Sedition, reprograms the mission's robot to destroy the ship. He is betrayed, though, by his employers and left as an unwilling stowaway when the "Jupiter II" blasts off.