The basic plots of the books are the same: uncovering secret identities.
In The Forgotten Garden, Nell and her granddaughter search Nell's past to learn how she arrived in Australia as an unattended child. The Winter Garden focuses on sisters Meredith and Nina who realize their Russian-born mother's fairy tales contain as much fact as fantasy.
Which made me think about 20 Master Plots (And How to Build Them) by Ronald B. Tobias. In the first chapter of the book, Tobias addresses different responses to the question "How many plots are there?" For the purposes of his book, he settles on twenty. Tobias defines "story" as a chronicle of events -- a narration of events in the sequence that they happened. He distinguishes "plot" as a story that has a pattern of action and reaction -- a chain of cause-and-effect relationships that constantly create a pattern of unified action and behavior. Plot adds "why?" to the story questions of "who?" and "what?"
So which master plot describes the two Garden books? I'm guessing Master Plot #7: The Riddle. This is the basic mystery plot. Tobias begins the chapter with a quote by Mary Roberts Rinehart: The mystery story is really two stories in one: the story of what happened and the story of what appeared to happen.
Rinehart, a master of mystery and suspense, sums it up quite neatly.
In The Forgotten Garden, it appears that a four-year-old girl has been abandoned by her family. I won't reveal what actually occurred in case anyone wants to read the novel. In Winter Garden, it appears to Meredith and Nina that their mother is cold and reserved -- saving her love and affection for only their father, Evan. The reality they uncover changes all their lives.
Which only goes to show, different writers can take the same basic plot (searching for a woman's secret past) and develop it in their own unique fashion.
Which in turn brings me to editor and agent workshops I've attended at the Willamette Writers Conference. Just when you think dragons, vampires, and zombies have been over done -- some writer takes the same basic plot into a whole new direction that catches everyone's imagination.
Dickens wrote the classic novel about an orphaned boy (Oliver Twist). Then came J. K. Rowling.
So...no writer should become discouraged by trying to come up with a brand new, never-been-done-before plot. Write your own version of one of the Master Plots.