Preheat the oven to 400 degrees.
Combine the celery seed and caraway seeds on a shallow plate and set aside. Brush the tenderloins with mustard all over. Season with salt and pepper and roll into the spice mix. Lay a sage sprig on each loin and truss every inch.
In an ovenproof skillet over high heat, add the olive oil. Sear the loins on one side for about 1 minute. Turn the pork and place in the oven. Roast for about 7 to 9 minutes; turn and roast for 7 to 9 minutes more. The tenderloin will be medium when the internal temperature, taken with a meat thermometer, is 145 degrees for medium, 150 degrees for medium well.
Remove the meat to a cutting board and let rest for 10 minutes. Cut into 1/2-inch slices. Arrange 3 slices on each plate and serve with the Seared Plums.