In a small saucepan, combine 1 cup water, half of the mint leaves, the sugar, vinegar and pepper. Bring to a boil, then lower the heat and simmer for 5 minutes.
In a small bowl, stir together the cornstarch and 4 teaspoons water. Stir into the saucepan and bring to a boil. Remove from the heat and let cool for 10 minutes; strain.
In a large bowl, toss the dressing with the honeydew, cantaloupe, peaches, strawberries and raspberries. Top with the remaining mint leaves.