Sian Barbara Allen guest-stars as the tenacious-and very pregnant-Teresa Burnside. Despite the imminent birth of her child, Teresa defiantly stands up to a gang of outlaws, who plan to use her as a pawn in a holdup scheme. As the crooks hold Teresa's husband Vance (James Olson) hostage, Ben Cartwright assumes the responsibility of delivering her baby. Also in the cast are Murray McLeod as Zachariah and Albert Salmi as Stretch. First shown on October 24, 1972, "Ambush at Rio Lobo" was written by Joel Murcott. ~ Hal Erickson, Rovi