Don't go up to one and be ruthless? (4,2,7)
I believe the answer is:
stop at nothing
'ruthless?' is the definition.
Both the answer and definition are adjectives.
Perhaps there's an association between them I don't understand?
'don't go up to one and' is the wordplay.
I cannot really understand how this works, but
'to' is within the answer.
'one' could be 'o' (I've seen this in other clues) and 'o' is found in the answer.
'and' could be 'n' (common abbreviation for 'and') and 'n' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
'be' acts as a link.
Can you help me to learn more?
(Other definitions for stop at nothing that I've seen before include "Act ruthlessly" , "as announcers of rocket launches do?" , "Be totally ruthless" , "3 [COUNTDOWN CONUMDRUM] will" , "Ignore all scruples" .)