Grandma and Grandpa Larsen were revealed to have 'died' because of a gas leak while visiting Uncle Tuck and Aunt Kim in South Carolina. Seth and Kendra's parents, along with other relatives, were sent on a 17-day Scandinavian cruise. This resulted in Kendra and Seth having to stay at Fablehaven.
Keys to the Demon Prison
Grandma Larsen visited Fablehaven in disguise, and using the Chronometer, traveled back in time with Grandma and Grandpa Sorenson, Kendra, and Warren. Back in time, she pulled off her mask and revealed herself. She told Kendra her parents had actually buried stingbulbs, and that Grandpa Larsen was assistant caretaker at Living Mirage, spying on the Sphinx. It is also revealed that their identity was blown by Vanessa Santoro, when she saw a home movie of them with Kendra and Seth. Hank helped plan an escape for Scott and Marla Sorenson.
Grandpa and Grandma Larsen become the new caretakers of Fablehaven while Grandma and Grandpa Sorenson accompany Kendra and Seth to Wyrmroost.