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'The Fortification Implementation' - Season 8, Episode 20
When Sheldon feels down about being left out of a physics symposium, Amy suggests they spend their date night building a fort. Meanwhile, after Howard gets the title deed to his mother's old house, he is surprised when an unknown relative turns up on his doorstep. Meanwhile, when Penny appears on Wil Wheaton's podcast, she and Leonard have a big on-air fight.
Air Date: April 9, 2015.