Book I

 Journeys to Camelot: Merlin Sails the Seas of Time

Merlin is sent by the Council of Elders to the future to find the aid promised by an ancient prophecy. What he finds seems unlikely to help: five couch-potato-type members of one extended family. He takes them back to the fifth century, King Arthur's time, to combat an evil sorceress. She wants to kill a young lad who promises to be a great white wizard if he survives. 

Merlin loses them when bringing them back to his time. They are on their own and are confronted with changeling-trolls, wolves, shape-shifters, and an army of assassins.  He manages to rescue them from imminent death only to inform them that an elaborate trap has been set for the shamaness, and they are an important, if reluctant part.