iCal disappeared

I tried to open iCal today, and a question mark appeared over the icon in my dock. Being the brilliant person I am, I figured that means the computer doesn't know what that icon is for. I right clicked it and the only option was "remove from dock", which I did, figuring I'd have to put it back from the applications folder. I tried to open it from my applications folder but it is not there. I searched for it in Finder and came up empty. Other users on the same computer still have their iCal. What could have happened to it and how do I get it back? I haven't been changing settings or anything. It was working fine a yesterday.