Sprinkle fish with salt and pepper; fold in half. Place fish in 10-ince skillet; add wine, water, shallots and lemon juice. Heat to boiling; reduce heat. Cover and simmer until fish flakes easily with fork, 4 - 5 minutes. Remove with slotted spatula to heatproof platter, keep warm. Add grapes to liquid in skillet. Heat to boiling; reduce heat. Simmer uncovered 3 minutes. Remove grapes with slotted spoon.
Heat liquid in skillet to boiling; boil until reduced to 1 cup. Pour liquid into measuring cup; reserve. Heat 2 Tbl butter in skillet until melted; stir in flour. Cook and stir 1 minute; remove from heat. Stir in reserved liquid and the whipping cream. Heat to boiling, stirring constantly.
Boil and stir 1 minute. Add 2 Tbl butter, stir until melted. Drain excess liquid from fish; spoon sauce over fish. Set oven to broil. Broil fish 4 inches from heat just until sauce is glazed, about 3 minutes. Garnish with grapes.