Return to default error handling
Just re-throw the exception and pretend like nothing ever happened...

try
{
    // Some code which might produce an error
}
catch (\Exception $e)
{
    if (craft()-&gt;request-&gt;isCpRequest()) {
        // Do something with $e-&gt;getMessage()
    } else {
        // Nothing to see here...
        throw $e;
    }
}