Some of the wordplay was a bit obscure this week, or is my brain giving in? I am left with 18D: One unexpectedly does right in America. I have N?O?O?S assuming that 17A (To hand over service, make fresh poster) is "ON ONES DOORSTEP. I can't follow the logic on that: I can see that the answer is "to hand" and that the last six letters are an anagram of "POSTER" but I don't see the front end at all. Any enlightenment and explanation will be very gratefully received