Written in Sand.A mysterious nanite-free zone appears in the midst of a massive storm in the desert. Rex is sent to investigate, discovering that Van Kleiss and the Pack are also present. Rex and Van Kleiss are sucked underground, and agree to put aside their differences temporarily in order to investigate the source of the nanite-free storm, which Van Kleiss sees as a threat to his EVO existence. As they travel deeper, they realize that their nanites are being slowly destroyed, causing them both to waste away. As they both may perish, Van Kleiss convinces Rex to play a game of quid pro quo for each other's knowledge. Van Kleiss then claims that Caesar was the one responsible for the Nanite Event. An enraged Rex accidentally activates a security system built into the rocks, and the two realize that the whole area is a circuit board. Rex deduces that the source is ZAG-RS, who survived reentry in their previous encounter in space, and is now attempting to destroy all nanites using the storm. Van Kleiss reveals that Rex's Omega-1 nanite can self-replicate, creating new nanites, and Rex uses this knowledge to fight back against ZAG-RS until Van Kleiss deactivates her and vanishes. ZAG-RS is taken into Providence custody, and Caesar reveals that he originally designed her to eliminate stray nanites, and that her voice is that of Rex's mother, Violetta.