Simple penniless fellow returned, with money in pockets? Certainly (3,2,7)
I believe the answer is:
and no mistake
'certainly' is the definition.
(thesaurus)
'simple penniless fellow returned with money in pockets?' is the wordplay.
I cannot quite see how this works, but
'with' could be 'and' and 'and' is present in the answer.
'money' could be 'm' (abbreviation used in economics) and 'm' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for and no mistake that I've seen before include "Assuredly (informal)" , "Without any doubt" .)