Install of in_place_editing not working

I have recently upgraded by application to 2.2.2.

In doing so, I have installed the plugin in_place_editing from github
using:

ruby script/plugin install git://github.com/rails/in_place_editing.git

I now see an executable file under vendor/plugins called
in_place_editing.git

But when I try to execute my code, I get the following error:

undefined method `in_place_edit_for’ for BaseController:Class

I suspect the plugin has not been installed correctly.

Any thoughts appreciated.