Across:
   7. Strangely, I forgot to dive in (2 3 2)
   8. Crossword master with cross to bear - I'm seen as eccentric (7)
  10. Gear man inclined to possess? (6)
  11. Explorer went past it, ten paces off (8)
  12. Backing a deity (4)
  13. Pile made from clue - am cut a deal (10)
  15,19dn. How tie's hue affected leader's address (5 5)
  16. Stay empowered following cult leader (5)
  21. Educator is not Rome's disgrace (10)
  23. Crazy lark with one of the Marx brothers (4)
  24. They're stepped on publicly, i.e. overwhelmed by internet bullies (8)
  26. Honours good competition (6)
  27. Like cat o'nine tails, the Italian version (7)
  28,20dn. Bombs ... near lunar scale! (7 7)
Down:
   1. If heroic, our agents must have this (7)
   2. Feminine desire conquering country (8)
   3. Invite lags to become enforcers (10)
   4. Thin cryptic clue (4)
   5. Made pile controlling oddly nice device for solving crossword (6)
   6. In trip, see change - good as holiday! (7)
   9. Implement when bent can easily cut in reverse (5)
  14. Nasty one flung about, sending a message (10)
  17. Facebook posts aim to be this perverted bleak lie (8)
  18. Thus cures ills where they begin (7)
  19. see 15ac
  20. see 28ac
  22. Some congenital entertainment ability (6)
  25. Possible end of reductions? (4)