As Witto suggests..

It should look like one of these.
 Code:
Local Lan -> Cisco Router -> Remote Lan
                  |
                  V
               FireWall -> Internet

 Code:
Local Lan -> Firewall -> Cisco Router -> Internet
                              |
                              V
                          Remote Lan


Dependent on if you "trust" your Remote Lan, then all of your clients have a single default gateway and the Cisco Router is then doing as it is designed - routing.
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