Complete story — includes the ending
While Ben, Gwen, and Kevin are taking a break at Max's favorite fishing spot, they see a mysterious cloaked elderly woman leave a pink-and-yellow flower at the base of a nearby tree that depicts the romance sign "Max + Verdona".
When the team tries to meet her, she disappears in a sudden flash of pink/magenta-colored light. They decide to stake out the area for a while until the elderly woman shows up again. When she reappears, Ben and Kevin confront her, and she is revealed to possess magical powers exactly like Gwen's. However, when she sees Gwen use her powers against her, she is amazed.
Gwen's innate magical/mystical powers are revealed to be had been inherited from the strange woman - Ben and Gwen's long-lost paternal grandmother, Max's wife, as well as the mother of Carl and Frank, Verdona, who is an immensely powerful energy being called an anodite from the distant world Anodyne. Verdona attempts to convince Gwen to break out of her human body and embrace her full strength and abilities of her innermost anodite self, but Gwen adamantly refuses. Verdona reluctantly leaves, but promises to return to visit now and then. Omnitrix alien debuts: Spidermonkey
Sources and content license
Source and revision history · Adapted from Wikipedia contributors, List of Ben 10: Alien Force episodes. HTML formatting and reference markers removed. · Content license