Clockwise round the grid run six of a kind (one of three words and one three-word pair). Other unclued lights show where you might find others of their kind. Unchecked corner letters could give PLAY-DEN PLANK.
 

Across

11    With everyone away, call hourly for singers (6)
13    Old bird biting end off confectionery (3)
16    Group of people, just the first section (5)
17    Left in the rain, following ordinary bird (5)
18    Power to clear out stretch of land (6)
19    Joke about family breaking up (6)
20    Develop strong emotion, turning against English (6)
21    Bills from old masters (5)
22    New mentor works in vacation (7, hyphened)
28   ...