Lot returned with nothing in it but a work instrument (4)
I believe the answer is:
tool
'instrument' is the definition.
(I know that instrument can be written as tool)
'lot returned with nothing' is the wordplay.
'returned' is a reversal indicator.
'with' is an insertion indicator.
'nothing' becomes 'O' (looks like zero - 0).
'lot' backwards is 'tol'.
'tol' enclosing 'o' is 'TOOL'.
'in it but a work' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for tool that I've seen before include "Implement - agency" , "Instrument, implement" , "Maybe saw" , "Appliance" , "Person exploited" .)