When Sheldon decides to take his non-relationship to the next level by procreating with Amy, Penny suggested they should at least try dating first.  Hence, she finds herself driving and chaperoning the two socially inept nerds.

Meanwhile, Howard steals a robotic arm he built for the space station and decides to use it to try and give himself a massage... and eventually moves it downstairs.  Soon, Howard finds himself calling the guys for help and at the hospital.  A reboot ultimately solves his problem.