jQuery Grid Plugin - jqGrid

I have a typical master/detail pair of jqGrids on a page.

My problem is that if the page is not interacted with for sometime the session times out. When the user comes back to the page and selects a different row in the master table a new request for data for the detail grid is made to the server.

I use struts on the server side, so it intercepts a call for the the detail json data and sends a login form instead. My issue is that this data ends up inside jqGrid, and all I see is that the data does not load on the grid. How can I trap this and redirect the page to my login page.