The Time Tunnel - Season 1 Episode 27 Merlin the Magician

Tony and Doug are frozen in time, then a rather fey Merlin appears in the Project base. He takes the guys out of time and freezes them, commands them to do his bidding, then sends them on to 544 A.D., Cornwall England. They meet a young pre-King Arthur while fighting Vikings and on Merlin's behest team up with Arthur. The Vikings apparently kill Doug and capture Tony and Arthur. Tony escapes with Arthur and Doug is rescued by Merlin and Guienvere. When the Project staff are ready to recover Doug and Tony, Merlin intervenes because he needs them where they are. Tony and Arthur get recaptured and so does Doug when he goes to help. Guinevere gets captured too. One of the Vikings kills Arthur and a ""detained"" Merlin shows up and reverses time to save him. The guys escape again and Doug gets reinforcements which Merlin disguises as Vikings while Arthur and Tony rescue Guinevere. Everything works out and Arthur and Guinevere are to be married.