Preakness Stakes Contender Profile Pletcher’s River Thames Looks to Make History   Hall of Fame trainer Todd Pletcher is back at Pimlico with one of his most promising Preakness starters yet. Instead of taking a shot in the Kentucky Derby, River Thames was held back in favor of a focused run at the 150th Preakness Stakes, a decision that may pay off with a well-rested and steadily improving colt.