How to Make It
Using a sharp knife, peel the grapefruit, removing all of the bitter white pith. Working over a bowl, cut in between the membranes to release the sections. Squeeze the juice from the membrane into another bowl; you should have about 3 tablespoons of juice.
In a large skillet, cook the bacon over moderate heat until crisp, 3 minutes. Using a slotted spoon, transfer it to a small plate. Pour off all but 1 tablespoon of the bacon fat.
Season the scallops with salt and pepper, add to the skillet and cook over moderately high heat until browned, 3 minutes. Turn the scallops, add the onion and cook over moderate heat until the scallops are just cooked through, 3 minutes longer. Transfer to a plate.
Add the wine and grapefruit juice to the skillet and bring to a simmer over moderate heat. Cook, scraping up any browned bits. Strain the liquid into a heatproof cup, then return it to the skillet. Add the capers and butter and cook, shaking the pan, until the sauce is thickened, 2 to 3 minutes. Add the scallops and any juices to the skillet; turn to coat them with the sauce. Add the grapefruit sections and bacon and serve right away.