Unclued lights can be arranged so that, preceded by ‘What is’, they form a question whose answer solvers must shade. Ignore a hyphen.

Across

1 Matlows flying from atelier on fire in hacienda (11, three words)

11 Fish swimming again around noon (6)

13 First son wrestles with eighth (7)

15 A punch followed by a little uppercut later (5)

17 Priest is protecting aged trees (6)

18 Science journal grandchild takes (5)

20 Heartless Brummie tarnished silvery stuff (6)

21 Absurdist philosopher backs into tree (5)

27 Georgia, twisted girl, getting hot in hell (7)

29 Poor...