Cooking frozen mussels
I always buy frozen mussels. I buy the ones that are in the half shell though. You're supposed to cook them from frozen, in the oven (375 or 400?) for 12 mins or so.
They're quite good and high in iron. Before baking I put some seasoned butter on all of them, or olive oil and garlic. Whatever you want really then I squeeze lemon over them when they come out.
If yours are closed I'm really not sure what you could do, I'd thaw them overnight in the fridge them throw them in a big pot with a bit of boiled water in the bottom and close, let us know if they open up.
Must admit, I've never seen frozen mussels so I'm curious to know the answer. Although they are obviously dead (as in frozen to death), my guess is that the ones which were alive beforehand should open as normal and the ones that were dead before won't open so should be chucked away.
If you don't get a definitive answer before dinner, please let us know what happened - perhaps when you're back from the hospital. :-0