Across:
   1.  He's suing a range of characters for his troubles (9)
   6.  More like the kind of queen to follow 5cc (5)
   9.  Nasty label from one who favours abuse over proof? (7)
  10.  Found in expanded DNA: cryptic clue in head of chromosome (7)
  11.  Side as night and day? (8)
  13.  Go ahead, take the piss! Return the slander! (6)
  15.  King of a strange dark place? (5)
  16.  Direction of road after 26 articles (9)
  17.  Does even better than a pure blend with four Sulfur atoms mixed in (9)
  19.  Lines about monkey in a flap (5)
  21.  22 / 4 (6)
  22.  Side as night and day? (8)
  24.  The rest is some leader getting wood (7)
  25.  Substantial devastation in Zone 26 (7)
  27.  Lazes, about to move neither forwards nor backwards (5)
  28.  Stir it according to recipe following gas or stomach upset (9)
Down:
   1.  Passes for goals, perhaps, being around central intelligence leaders and holding prize for being greatest systems' analysts (15)
   2.  Rallied about leading union member, molested (7)
   3.  As with a disease, I will be contracted thus! (3)
   4.  The pens you built to one side with no right corners (10)
   5.  11 / 4 (4)
   6.  Finding someone dead gorgeous once hair lip operated on (11)
   7.  Some footballers at a famous garden show (7)
   8.  Religious teaching surrenders accounts that are short (15)
  12.  USA in stable deal that could continue indefinitely (11)
  14.  In the surge, I push in for the US bosses (10)
  18.  Echo is more so under the main span (7)
  20.  Excuse prior to writing (7)
  23.  Kind of queen that's racy?  (4)
  26.  When neither is seen, this may soon appear (3)