Infiltrators Team Retribution screens for among the mages working on the Nest.
Carl posts two crawlers from Elle's team beside the newly-arrived mages laying protections on The Nest, to make certain they aren't spies or worm heads. The concern is real enough to justify the manpower during the last two hours before Open Hostilities, because everything about Operation Ruin depends on the tower and nothing about it can be concealed.
Drick, notably, is a Valtay worm himself — which is why Carl finds it interesting that he smells like he's been overindulging at the bar with Ferdinand.
The infiltration threat Team Retribution screens its work crews against.