This is probably not a fly you've heard of for saltwater use but I had some sent by a friend in Canada where they use them for Char and Salmon in arctic rivers and lakes. One day I was having no success on my usual flies as the water was a bit murky, so I tied on this fly and had instant results 
My version is much, much simpler than the original flies I was sent and I've cheated slightly by using mylar tube for the body, but it works just as well I think.
It's tied on a standard long shank hook (a Kamasan B940 size 1/0 in this example) using red thread to start with, taking it down to the bend in the hook:
Slide a tube of silver mylar over the shank of the hook and tie it on at the end by the bend, building up a tapered end then whip finish and cut off the thread. It's worth putting a spot of superglue in the end of the mylar tube before tying it on the keep it firmly in place. In the original fly the body was wrapped in silver tinsel and not mylar tube as I've used!
Change to black thread, stretch the mylar tube tightly to the hook eye and whip into place with the black thread. Once again a spot of superglue can be used to keep the tube in place.
The top wing is a mixed bunch of red and yellow bucktail with a few strands of gold-coloured flash added. The original flies had these tied in layers of yellow, red then yellow again but I'm lazy and find that a mixture of coloured bucktail with some added flash works just as well. ( This is where the 'Lazy' bit in the title comes from!) Whip all this down with the black thread and created a tapered head, then whip finish. The wing should project well beyond the bend of the hook
To finish off the fly put a nice shiny blob of epoxy on the red whipping and also coat the head in epoxy or several layers of varnish. Its a very simple and old-fashioned pattern but seems to work well in poor conditions when other flies fail.
Below - the almost finished fly still needing the head epoxying:
P.S. Don't ask me why it's called the Mickey Finn as I have no idea 
Allegedly it was invented in the 1930s around the time Rudolph Valentino was killed by a poisoned drink, a Mickey Finn. The fly had been known as the "Red & Yellow" or the "Assassin" but it was nicknamed the "Mickey Finn" because of Valentino and the name stuck...
(Thank you Google) 
