Years of success, meticulous planning, and an eye for detail have in no way prepared Vivienne Avery for her mother’s slide into the grip of dementia. Vivienne recounts memories of her aging mother and the difficult decisions regarding her care. Interwoven with these stories is an evolving, wondrous 21st century Alzheimer’s creation myth — an origin story about a White Egret who tries to protect forest animals as they lose their memories to a blind, oblivious Mole. “Blackberry Winter” is a moving, occasionally humorous, and deeply human new work.