And one is heartless with the girl (4)
I believe the answer is:
anne
'girl' is the definition.
(girl's name)
'and one is heartless' is the wordplay.
I cannot quite understand how this works, but
'and' could be 'n' (common abbreviation for 'and') and 'n' is present in the answer.
'one' could be 'ane' (synonyms) and 'ane' is located in the leftover letters.
No letters remain.
This explanation may well be incorrect...
'with the' is the link.
Can you help me to learn more?
(Other definitions for anne that I've seen before include "Queen in 1702-14" , "Second or fourth wife of Henry VIII" , "First queen of Great Britain and Ireland" , "Henry's second" , "She married Shakespeare" .)