Am stuck on the last three viz 7D (5,7) one of this US poet's 2 plays was an attraction for many ?A??? M?R?B?N 17D (7) repeatedly heard from 9 in operetta T?R?T?A (my answer to 9ac is trumpet) and 18D (7) catch on to different meaning for action of faction writer - [the b, r and u presumes that my answer to 21 A (where Pickwick found a valet - ie Borough) is the answer looked for] Can anyone throw any light on the above?