Henry unravels previous clue without reading first - that's rapid (5)
I believe the answer is:
hasty
'rapid' is the definition.
(thesaurus)
'henry unravels previous clue without reading first' is the wordplay.
I cannot quite understand how this works, but
'henry' could be 'h' (symbol for the unit of electrical inductance) and 'h' is located in the answer.
'first' could be 'a' (first letter of the alphabet) and 'a' is found within the answer.
The remaining letters 'sty' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for hasty that I've seen before include "Reckless; hurried" , "Rushed; rash" , "Too hurried, careless" , "Too quick, impetuous" , "Quick - reckless" .)