Across:
   1. Penny, trapped in bizarre safe, is gradually forgotten (5)
   4. Celebrated with Mecca laid out (9)
   9. Rewrote notes in case of court challenge (7)
  10. Dragnet happened to include Ms Fältskog (7)
  11. Taking a plunge, sixth moves to first, almost causing a boilover (9)
  12. Flip boundaries with inclusion of odd woman, not 14 (5)
  13. Originally 10, 24, 28, 6? (4)
  15. Venus or Io? I muddle stars sometimes, seen in this 19 9 (10)
  18. Came back to life when at sea, a keen wader (10)
  19. Slow nags regularly go for one? (4)
  22. Let it learn to have a name (5)
  23. Some of returned caramel bar is edible, so you might want it (9)
  25. With hackles perhaps raised, ran away, unsettled (7)
  26. Pissed off rant giving offence (7)
  27. Turn up with student paramours in casual clothes (9)
  28. Mr Andersson? He is big in London and New York (5)
Down:
   1. Eating duck heart, exotic fish and a flowering shrub (7)
   2. Stride nimbly sporting some strides made of this? (5)
   3. Country Poles smuggling crazy weed (6)
   4. Quality butter I churned at beginning (9)
   5. Sound used in Germanic languages (5)
   6. Schumann, if ridiculed, kept heart for Ms Lyngstad (4-4)
   7. Amount is such fiction, even for emperor (9)
   8. Straight, and aped carefully (7)
  14. Nice having gold fit back into blue fitting (9)
  16. Hangs around longer than rest, Savoy crazy (9)
  17. Law to Roe: sorry! 13 won 15 with this! (8)
  18. Geldof-penned hit role: sailor returning (3 4)
  20. "Break a leg!" ... "Try a lot!" (7)
  21. Fear P.B. will have to be beaten, having been made already (6)
  23. Avoid party having dull start with flipping for example (5)
  24. American head or normal head for Mr Ulvaeus? (5)