Three clues have no definition. Hints to 16d may be seen in other clues and solutions
Across
1 Fancied hotel client in audition (7) 5 Shouting about missing one report (7) 9 Exercises in pitch gradually tail off (5) 10 16 - I'm not sure after seeing old flame taken in by a state (9) 11 People arguing case, putting fences across street (10) 12 Millions put on main vein (4) 14 Tight social unit on for shots (12) 18 Shock second Democrat enveloped in suspicion getting tiny margin (5-7) 21 Sources of grief are those expecting attendance money (4) 22 State of mind after 16's economic failure (10) 25 Is tea sure to be served where flowers go? (9) 26 Short picture - origin of only adult version (5) 27 Call it English for a bug! (7) 28 Talk about quiet mother's face-covering (7)