Creep inside left... (5)
I believe the answer is:
sidle
'creep' is the definition.
(both can mean to move secretly or quietly)
'left' is the wordplay.
I cannot quite understand how this works, but
'left' could be 'l' (common abbreviation) and 'l' is found within the answer.
The remaining letters 'side' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'inside' is the link.
Can you help me to learn more?
(Other definitions for sidle that I've seen before include "sidewalk" , "Walk crabwise" , "Make cautious progress" , "Inch along" , "Slide (anag.)" .)