Ambush on an Imperial construction module

"I've never seen an orbital construction field this big."

- Sabine Wren

A few years before the Battle of Yavin, the Lothal rebels along with retired Clone trooper Rex participated in a mission to acquire information stored aboard an Imperial construction module in orbit around the desert planet of Geonosis. According to intelligence gathered by the rebellion, the information detailed what the Empire was building above the planet. Before the rebels could acquire the information, however, they were caught in an ambush by a several stormtroopers led by ISB Agent Kallus.

Prelude
After the conclusion of the Clone Wars construction of the Ultimate Weapon, later known as the Death Star, commenced in orbit above Geonosis. To keep the construction of the battlestation a secret, the Empire decided to wipe out the entirety of the Geonosian species. Some time later, at least 3 years before the Battle of Yavin, rebel intelligence discovered that the Empire was once building something above Geonosis, and so sent the Lothal Rebels to investigate.

The Mission
After arriving above the planet in the Ghost, the rebels quickly discovered that the Empire was indeed once building something there. A lifeform scan conducted by C1-10P revealed that the planet was devoid of life, much to the confusion of the rebels. The rebels decided to continue on with the mission and arrived at the construction module where Kanan, Ezra, Sabine and Zeb departed and went searching for the information.

Imperial ambush
An Imperial astromech droid spotted the rebels and informed Agent Kallus, who proceeded to ambush the rebels. A firefight broke out while the Imperial astromech closed the blast doors on the rebels, the droid was soon dispatched by C1-10P, however, when he electrocuted the droid and reopened the blast doors. Kanan, Ezra, Sabine and C1-10P managed to escape back to the Ghost, but Zeb was trapped in combat with Kallus. Zeb managed to enter an escape pod, but Kallus caught up with him before the pod was released. Once out of the hangar, the crew of the Ghost became engaged in combat with three AT-DPs and three TIE fighters. The fighting continued inside the pod, causing one of the controls to break and one of the pod's engines to malfunction. Changing course, the pod crash landed in a cave on the ice moon of Bahryn.

Surviving on the moon
After exiting the crashed pod, Zeb and the wounded Kallus decided it was best to work together if they were to survive, using a power generator and what they assumed was a meteorite to keep warm. Zeb repaired a transponder, but realized the signal wasn't powerful enough to get through the thick ice. A short time later, the pair were attacked by a huge beast called a bonzami, who they managed to fend off. Knowing the beast would come back, they attempted to escape by climbing the ice pillars supporting the cave. During their escape, the bonzami came back with another with it, however, despite the beast's efforts, Zeb and Kallus managed to narrowly escape through the hole punched in the cave's ceiling. Re-activating the transponder, the pair waited until the rebels eventually found their location. Believing it be best he waited for the Empire to retrieve him, Kallus opted to remain behind on the moon. The pair said their farewells and Zeb left to board the Ghost.

Aftermath
After arriving back aboard a Star Destroyer, Kallus was coldly greeted by Admiral Konstantine, in contrast to the way Zeb was greeted back by his fellow rebels. Acquiring a new perspective on the Empire and the rebellion, Kallus retreated to his quarters, conflicted on his view of the fight against the rebellion.