5 files should be acquired if you own the DLC:
[ul]
[li]brink agents of change dlc.ncf located in [B]…\Steam\steamapps[/B][/li][li]zzzdlc000.sdmd2 located in …\Steam\steamapps\common\brink\base[/li][li]zzzdlc000.sdpk2 located in …\Steam\steamapps\common\brink\base[/li][li]zzzdlcenglish000.sdmd2 located in …\Steam\steamapps\common\brink\base[/li][li]zzzdlcenglish000.sdpk2 located in …\Steam\steamapps\common\brink\base[/li][/ul]
Note that other languages would acquire different files to zzzdlcenglish000.sdmd2 and zzzdlcenglish000.sdpk2. E.g. French would acquire zzzdlcfrench000.sdmd2 and zzzdlcfrench000.sdpk2.
If you have any issues, verifying the local game cache for Brink in Steam should be your first course of action.