I went to Changeling on Wednesday night and I thought it was incredibly well told - if a little harrowing.
I am not a fan of Angelina Jolie but I think she played the part of Christine Collins very well - emotional and yet restrained as women of the 1920's probably would have been.
The story is basically thus
(contains spoilers):
CC (Christine Collins) goes to work leaving her 9yo son at home and when she comes back he has vanished. A few months down the track the LAPD are facing accusations that they are corrupt and incompetent, so when a boy turns up claiming to be CCs son, they see it as a chance to clear up their reputation. Except it is not CC's son and she trys to explain that to the LAPD. Eventually she goes to the Press and then the LAPD get mad and place her in an asylum.
At the same time a boy is captured for illegal immigration and confesses that he was forced into helping his uncle kill children out on his ranch, and that CC's son is amongst them.
CC is released and then the story follows what happens in the subsequent trial of both the LAPD and the uncle that killed the children. It was also not proven for definite at the time that CC's son was amongst those children and it follows her search for him.
I found it a bit difficult to see as a mother of a son, but worth seeing IYSWIM. I think that even dhs or dps would enjoy it too.