Perhaps Idomeneo and Flavio hope to undress before Overture to Swan Lake (5,5)

'perhaps idomeneo and flavio hope to undress' is the definition.
I know nothing about this answer so I can't judge whether this works.

'before overture to swan lake' is the wordplay.
I cannot quite see how this works, but
'before' could be 'ere' (usually literary) and 'ere' is found in the answer.
'lake' could be 'erie' (Lake Erie is one of the Canadian/US 'Great Lakes') and 'erie' is present in the answer.
The remaining letters 'ops' 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?