Express Big Monday
Having a spot of bother with a couple of intersecting ones. Surely 21A - Large northern constellation in which the Plough, or Big Dipper, is located (4,5) - should be Great Bear, but I can't get it to fit with 7D - 1958 Graham Greene espionage novel featuring vacuum cleaner salesman James Wormold (3,3,2,6) - for which I have Our Man in Havana, which I'm sure is right. But if it is, Bear would begin with an A!
As I don't think this has been asked before, it must be staring me in the face. Can anyone rescue me from this final headache? Blessings on you if you can!