Darkness falls over Cybertron as the legendary Onyx Prime returns throwing the planet into chaos! What does this mean for Optimus Prime--and Earth? As Onyx & his comrades sow panic & dissension on Cybertron Windblade defends an already tense planet against a secret that could shatter it forever while Soundwave questions a fragile alliance & Optimus confronts a mystery that goes back millions of years Collects Transformers Optimus Prime issues 15-21