Trouble there is about that infernal debt? (4,2,3)
I believe the answer is:
hell to pay
'about that infernal debt?' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.
'trouble there' is the wordplay.
'trouble' becomes 'hell' (hell is a kind of trouble).
'there' becomes 'topay' (I can't justify this - if you can you should give a lot more credence to this answer).
'hell'+'topay'='HELL TO PAY'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for hell to pay that I've seen before include "leading to serious consequences" , "dire consequences" .)