The Doctor once again comes across River Song who is on a mysterious mission to locate the last of the Weeping Angels. The Angels have a unique way of hiding - they appear to be solid and immovable when anyone is looking at them. Only when they are alone are they able to move or attack. Amy finds the relationship between the Doctor and River to be quite interesting, particularly when she learns that at some point in the distant future, they are to be married! The Doctor thinks dealing with the last of the Angels should be a relatively easy task but realizes they are in trouble when they find they are replicating and that there is now an army of them.
—garykmcd