While Commander Cody and Captain Rex are on an inspection tour of outposts manned by rookie clones, they arrive on the Rishi moon just after an infiltration of commando droids sent by the Separatist fleet.
Their outpost overtaken, four surviving rookies hide out until the arrival of Cody and Rex, then try to retake their station.
The Separatist droids have wired the "All Clear" signal to run at all times. A Separatist invasion is underway and the Republic must be alerted.