ACROSS

 1  Sketches by Boz? (8, 6)

 9  Petroleum. (7)

10  This poor man advised “early to bed.” (7)

11  Scales in G-sharp. (6)

12  Seen flying against some buildings. (8)

14  Clear is the word for such desserts. (7)

15  Place of prominence in Montana. (5)

17  The duplication of these is a classic mathematical problem. (6)

19  Basis of the place for fair. (7)

21  The military caste is blue. (8)

23  Association, in which hardly anyone uses his hands. (6)

25  Is the plate colored, or only slightly so? (7)

26  No coming back after I follow little work in. (7)

27  Ill-tempered remark? (6-9)

DOWN

 1  Ape, crying a eulogy. (9)

 2  Cue for the pack to be shuffled in. (7)

 3  How a mat-man is pinned down? (9)

 4  Turned on a renegade. (4)

 5  Supersonic beat. (10)

 6  Topic of needlework. (5)

 7  Concerning a man that counteracts. (7)

 8  A 50-50 chance there are none. (4)

13  An auto would make him confess. (10)

15  Belt, and in a sort of boiler there’s a charge in each case. (9)

16  Acne, under a condition of lasting quality. (9)

18  Large stone found in Colorado. (7)

20  This might cause a draft. (7)

21  In a way, a drink is too much for the Parisians. (4)

22  A steamer does without them. (6)

24  The bark of the weft? (4)