Yalek infiltrated the new faction of the Cult of the Dragon led by Severin Silrajin. In 1489 DR, he was among a Cult contingent sent to establish an alliance with the great dragon Claugiyliamatar of Kryptgarden Forest. He reported to his Zhent masters all that happened and they gave the information to an adventuring party hired to defeat Old Gnawbones.
The adventurers ambushed some stolen cargo guarded by some cultists, one of which was Yalek. They probably identified him thanks to his V-shaped scar and spared him. After the skirmish, he would reveal that the cultists were in search of a magic item, the Green Dragon's Mask, which was in possession of the hobgoblin warlord Garbul.