Try the unpromising fish from old Home Secretary's lake? (5,2,6)

'try the unpromising' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.

'fish from old home secretary's lake?' is the wordplay.
I cannot really see how this works, but
'fish' could be 'catch' (synonyms) and 'catch' is found in the answer.
'home' could be 'at' (synonyms) and 'at' is found in the answer.
The remaining letters 'straws' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

Can you help me to learn more?