Despair when you mislay Bob (4,4)
I believe the answer is:
lose hope
'despair' is the definition.
(synonyms)
'you mislay bob' is the wordplay.
I cannot quite see how this works, but
'mislay' could be 'lose' (synonyms) and 'lose' is present in the answer.
The remaining letters 'hope' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'when' acts as a link.
Can you help me to learn more?
(Other definitions for lose hope that I've seen before include "Become pessimistic" , "Despair" .)