The most common and most likely answer to this crossword clue is the 5 plus 2 letter word CLEAR UP
I've seen this crossword clue in The Daily Telegraph
C
L
E
A
R
U
P
More clues leading to the result CLEAR UP
- Get brighter uniform in different parcel
- Become fine again? Explain
- Get better crack
- Solve first of conundrums humorist raised
- Explain Shakespearean entering competition
- Tidy profit out of bed
- Poor Clare, raised and put in order
- Sort out Shakespearean character in hollow
- Explain what ten can represent?
- Solve a mystery and become brighter
Buddy explains!

The straight part
We know that "Solve a mystery/become brighter" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case solve a mystery/become brighter = clear up.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.