Yeah, I think you have to play at least 5 turns before you can concede; there is an option to "force cancel" at my end, though, which has pretty much the same effect...
...but are you sure?! It's essentially The Assassins crossed with "British Bulldog", except that the only person you have to "get" (OK shoot, stab or blow up) before they reach "base' is Sterner, and everyone else is a bonus. Whatcha say...?