We learn in that episode that some of Mary's fondness memories are of Ellie sitting between Stephen and Mary on long drives they went on when Ellie was very young. It is mentioned that the Mustang has blue colored seats which were specially ordered by Stephen.
Relevance to plot Edit
After Chuck mentions to Ellie that their dad might have left something for her after he died, he left Chuck his secret base, Ellie starts looking over the classified pages where Stephen had communicated in code with Ellie when he was alive.
She notices that the same advert for a 1968 Ford Mustang has been posted for several weeks but dismisses it until Mary talks about the family owning one when Ellie was little. Ellie and Devon go to the address listed in the advert a pick up the car where Ellie finds a goodbye letter from her father. As the pair drive off in the car, the camera looks under one of the seats and sees one of Orion's Laptop.