Supernatural: On the Head of a Pin

"On the Head of a Pin" is the sixteenth episode of season four of TV series Supernatural and the sixty-ninth episode of the series overall. It was directed by Charles Beeson and written by producer Sera Gamble. It premiered on the CW Network on Thursday, March 19th, 2009. In this episode, Sam and Dean must team up with Ruby to find Anna, a girl who can listen in on angelic conversations... and who the demons want to acquire. Ruby seemingly betrays the Winchesters and takes off with Anna. Meanwhile, Sam fills Dean in on how he met Ruby during Dean's time in Hell.