I'll Be Watching You - S1.E8

A teenage boy (Ian) is afraid of heights, but when he believes that he has a guardian angel, Mark is sent to investigate. But Song Li and Mary discover that people who see their guardian angels have their guardians fade away after a while. And in a dangerous attempt to fight his fear of heights, Ian's guardian fades away, and Mark must help him get across a pole high in the air without his guardian.