I've got the author, nickname & verse but a few of the individual clues are baffling me.
5a Mistakenly deduce how nothing is lost in plant(7)
38a Round grub on top of azalea (4)
6d Department's friendly director took great risks(5)
Dear Ruth,
I've managed to finish it (I think). 5a is an anagram of 'deduce(h)(o)w'; 'nothing'is the (o), and (h) is the extra letter; the plant is one you wouldn't want.
38a: 'round' is the definition (a noun), 'grub' is in the verbal sense, and you drop one of two 'o's' in a 4-letter synonym; this is the extra letter.'Top of azalea' is the final letter; the solution is a Latin word for 'wheel' but in English no longer has that literal sense.
6d There is a 4-letter French département from which you remove the letter 'u' (the extra one)and insert 'i' for 'independent'. The definition is 'assistant'.
Phew. Can you help me in return with 10d? I think I know the answer (the proper noun referred to in the intro), but I can't see how 'Christian' comes in. Or is it Christian D(i)or?