Badly mistreat an old puffer? (5,5)
I believe the answer is:
steam train
'old puffer?' is the definition.
I know nothing about this answer so I can't tell whether this works.
'badly mistreat an' is the wordplay.
'badly' indicates an anagram (letters in the wrong order).
'mistreat'+'an'='mistreatan'
'mistreatan' anagrammed gives 'STEAM TRAIN'.
Can you help me to learn more?
(Other definitions for steam train that I've seen before include "that runs on-line?" , "Type of locomotive" .)