Preheat the oven to 425 degrees F.
Rinse the turkey, pat it dry, and season it inside and out with salt and pepper. Pack the neck cavity with 1 lemon wedge, 1 thyme sprig, and 1 slice of bread. Fold the neck skin under the body, and fasten it with a skewer. Fill the body cavity with apple, onion, 3 thyme sprigs, lemon wedge, and remaining slice of bread. Truss the turkey. Rub turkey with remaining 3 thyme sprigs, then rub turkey with softened butter. Place on rack in roasting pan.
Roast for 30 minutes, then reduce temperature to 325 degrees and add water to roasting pan. Roast the turkey, basting it every 20 minutes, for another 2 1/2 to 3 hours, or until a meat thermometer inserted in the fleshy part of the thigh registers 180 degrees and the juices run clear when the thigh is pierced. Transfer the turkey to a heated platter, reserving the juices in the roasting pan, discard the string, and keep the turkey warm, covered loosely with foil.
For the Gravy: Skim all the fat from the roasting pan juices, reserving 1/3 cup of the fat, and add the cider and vinegar to the pan. Deglaze the pan over moderately high heat, scraping up the brown bits, and boil the mixture until it is reduced by 1/2. In a saucepan, combine the reserved fat and the flour and cook the roux over moderately low heat, whisking, for 3 minutes. Add the cider mixture and the stock in a stream, whisking, bring the mixture to a boil, whisking, and simmer the gravy, stirring occasionally, for 10 minutes. Season the gravy with salt and pepper and transfer it to a heated sauceboat.
Garnish the turkey with the herb sprigs and serve it with the gravy.