Ep 4. The 2003 Approximation

Leonard and Penny's marriage may be on the rocks, but that's not stopping Sheldon from promptly moving out of their apartment and back into his own. This sudden change of address leaves Leonard feeling a bit lost and lonely without his best friend by his side. Meanwhile, Howard and Raj begin work on a new project for the Air Force, which leads to some unexpected consequences for their friendship. As Sheldon tries to adjust to his new-old living situation, he turns to some unexpected sources for comfort and guidance. All the while, tensions continue to simmer between him and his ex-roommate as they both attempt to navigate their separate but intertwined lives.