Mislead in a firm way (3)
I believe the answer is:
con
'mislead' is the definition.
(I've seen this in other clues)
'firm way' is the wordplay.
'firm' becomes 'co' (abbreviation for company).
'way' becomes 'n' (Compass direction - North).
'co'+'n'='CON'
'in a' acts as a link.
(Other definitions for con that I've seen before include "politician who's in the right" , "Not in favour" , "Deceive; convict (colloq.)" , "Study - swindle" , "Informally swindle" .)