How do I redirect within a ViewResult or ActionResult function?

Say I have:

public ViewResult List() 
{
    IEnumerable<IModel> myList = repository.GetMyList();
    if(1 == myList.Count())
    {
        RedirectToAction("Edit", new { id = myList.Single().id });
    }

    return View(myList);
}

Inside this function, I check if there is only one item in the list, if there is I'd like to redirect straight to the controller that handles the list item, otherwise I want to display the List View.

How do I do this? Simply adding a RedirectToAction doesn't work - the call is hit but VS just steps over it and tries to return the View at the bottom.