When they arrive at the monastery, the Monk feigns ignorance of the doctors location-which Vicki picks up as he already knows the doctors description without them having told him. While the Saxon's are in heavy preparation for the upcoming Viking invasion,Steven and Vicki locate an exotic weapon,actually a nuclear cannon, on the hill above the rocky beach. Believing the TARDIS to have been swept away in the upcoming tide, they arrive at the monastery to search for the doctor to find him missing. Upon further searching they locate a sarcophagus in the Monks cell and,upon entering it find that its actually a TARDIS. While reading of the Monks alterations of Earth's timeline, the doctor has also learned that the Monk is a time meddler whose intent is to destroy the Viking fleet to allow Kind Harold to be the victor in the upcoming Battle Of Hastings. With the Monk trying to fool the doctor again by selling him out to the invading Vikings,the doctor ends up reuniting with Vicki and Steven in the Monks TARDIS,a slightly more advanced model than the doctors. The monk,believing human society in Europe would improve centuries ahead of its intended time under King Harold-with the help of his more advanced technology. The monk escapes the invading Vikings again while the doctor removes the dimensional stabilizer in the Monk's TARDIS-leaving him stranded in 1066 as they escape in the TARDIS with the congrats of Edith,convinced only that they have successfully averted a Viking spy.
Before the term "time lord" was ever introduced into the Doctor Who lexicon, this was a story of major firsts for the series. Its the debut of Peter Purves' Steven Taylor as a companion. While beginning as an intense skeptic of what he sees around him,much to the doctors chagrin, he is soon finding himself confronting by a mystery that even confounds the doctor: a meddling Monk who is actually one of the doctors own people-as we'd learn later a fellow time lord. While his goals seem to be essentially benevolent in intention, there is a sense that he is doing it largely for his own sport and to alleviate the time lords code of non interference in the time line which,again without using the word time lord, as made very clear by the doctor in this story. Luckily the doctor is able to arrange things carefully so his confident Saxon allies Edith and Wulnoth only ever view the meddling Monk,of course with Petter Butterworth easily equaling Hartnell's performance as a fellow "time traveler". This is also one of the earliest stories pointing to the indestructibility of the TARDIS itself which, considering this is also the first story to contain more than one TARDIS makes this a very significant story to the progression of Doctor Who.