The setting is the tracking station on the Rishi moon, located on the wispy borders of Republic space, not far from the cloning facilities of Kamino.

Inside the station are a team of rookie clones. Hevy is the impetuous and impatient one. He whiles the time away arm-wrestling with trooper Cutup, the joker. Echo is all about regulation manuals and protocol. Also there is Fives (CT 27-5555), Nub (named after the non-flattering acronym "Non-Useful Body") and Droidbait.

Long range sensors detect an incoming meteor shower. The clones raise the defensive shields, which block any meteors that land too close, but several strike in the outlying crater plain. Within the craters is a droid landing pod from which emerges sleek and stealthy droid commandos!

When the perimeter scout fails to report in, a concerned Sergeant O'Niner sends Nub and Droidbait to investigate. They discover the infiltrating commando droids and are cut down by enemy fire. The clones attempt to activate the alert beacon, but the droids have disabled it. O'Niner is killed by droid fire, leaving only Fives, Echo, Cutup and Hevy behind to carry out the mission.

Just then, a Republic shuttle arrives at the Rishi outpost. Rex and Cody are on an inspection tour. A droid commando tries to fool them that all is okay at the outpost, but Rex sees through their charade.

The four rookie clones sneak out of the outpost through a ventilation shaft, and emerge in the crater-filled crags beneath the tracking station. They find no safety: an immense Rishi eel chomps down on Trooper Cutup, dragging him away screaming. The remaining three clones spot Cody's shuttle coming in for a landing. The rookies fire an alert flare to warn the officers of the droid invasion.

Below the platform, Rex and Cody discover the remaining rookies. The rookies briefly marvel at the officers' skill and bravery marksmanship, but quickly snap to attention as Cody takes command of them. The young clones, particularly Hevy, are determined to retake their outpost.

Rex and Cody lead the rookies in storming the ops center. In the gunfight, Fives is wounded, but the clones successfully wipe out the commandos. Cody examines the controls and detects the Separatist fleet invading Republic space. The Rishi base is transmitting a hard-wired all-clear signal, covering the Separatist approach.

Separatist reinforcements arrive in a landing craft. Rex improvises a new objective: the clones must destroy the outpost. When the all-clear signal stops broadcasting, the Republic will be alerted to the invasion. Echo suggests using liquid Tibanna fuel to blow up the base.

The clones retreat deeper into the station, holding off the droids long enough for their explosives to be set. Rex is having trouble with a faulty detonator. Hevy takes over demolition duty, telling Rex and the rest to evacuate through the vent shaft. Hevy has little luck with the detonator, but he's determined to manually detonate the explosives. He is blasted by the droids, but goes down fighting.

Dying, Hevy uses his last ounce of strength to trip the explosives, ripping the entire station apart in a fireball that sends the landing platform -- and the droid lander -- crashing into the crater. There is an immediate result -- the all clear signal stops. The Republic fleet realizes an invasion may be underway.

Later, aboard a Jedi cruiser, the surviving clone rookies -- Echo and Fives -- are commended for their service and their sacrifice. They receive medals directly from Generals Obi-Wan Kenobi and Anakin Skywalker and are absorbed into the 501st.