In arguably their most important quest yet, Ash and Tilly have to prevent Ragnarok! Yggdrasil, the world tree, is missing, and the Asgard Yuletide Committee needs a replacement to decorate for their upcoming Yule celebrations. Luckily, they are joined by return guest Genoveva Dimova, archaeobotanist and fantasy author. Together, they discuss the symbolism of trees in fantasy fiction and mythology and attempt to answer the ultimate question: which is the greatest tree of all?