What are some Nora Roberts trilogies?

Norah Roberts has authored several trilogies, including "The Sign of Seven Trilogy" and the "Circle Trilogy." Readers can also enjoy the "Three Sisters Trilogy" and the "Key Trilogy."

The "In the Garden" series is another trilogy written by Roberts. It follows the lives of three women who open a nursery on the property of an old mansion. They discover life-changing secrets inside of the old, historic home and must lean on one another to deal with their own personal tragedies.

"The Sign of Seven" trilogy offers an unexpected and darker side of Robert's writing. This series centers on three men who unwittingly unleashed a demon on their small town when they were boys. The stories document the paranormal activities that plague the town and how the protagonists attempt to save it.