1: A muskmelon or cola nut pa sliced (9)
2: Measure of heat in the empty room (5)
3: Reverse engineer, at last, recipe for dish best served cold? (7)
4: Pauses awkwardly after error but steadies nerves (5,2)
5: Free to turn some integral tables (2,5)
6: Elves distressed priests (7)
7: Ray is a guy who just loafs around, so people say (5)
10: Gymnast produces hybrid of car and boat (7)
12: Press or key source of metal (4,3)
13: Vile dingo disturbed in sinful act. (9)
15: Deciphered code in a sea-nymph (7)
16: Nearly nail half of veterans for childishness (7)
17: Chalet I remodeled in conformance with professional standards (7)
18: Any number follow festival in the Orient (7)
19: Fill-in professional almost rewrote the column (5)
21: Assistants' crackpot ideas (5)