Any help much appreciated with:-
13. Races round in order to give the outline of the plot (8)
21. Ducks and drakes used to bust the dam (8)
83. Only man without a grave (6)
99. Coat of metal obtained from excavation between meandering rivers (9)
I have a suspicion that the answer will be 'bouncers' which will fit both parts of the clue. I don't think that you can say that the 'u' is silent but the setter might have thought so.