The Tardis lands in the middle of the Holy Land during the time of the Crusades.
The Crusade is the second of the missing stories (sadly, there are a lot more of these to come throughout the First and Second Doctor era). Unlike the first missing story, Marco Polo, two of the episodes still exist and were made available on the Lost in Time DVD (see picture). Additionally, the DVD provides linking narration, provided by William Christopher (in character as Ian Chesterton). The audio portion of the missing episodes 2 and 4 are also provided on the DVD so that one may listen to the entire storyline.
Having recently watched this story a couple of month ago prior to starting my marathon viewing, I decided to watch the existing episodes with the provided linking narration by William Christopher as Ian, rather than listening to the entire audio soundtrack of the missing episodes. Let me just say that while I appreciate having the linking narration (and it's nice seeing William Christopher in character again as Ian), I think the actual audio soundtracks are definitely the way to go. The linking narration simply doesn't go into enough detail, particularly in regard to some of the may subplots.
The Crusade begins with the Tardis landing in a wooded area just outside of Jaffa. A Saracen raid is taking place, led by the Saracen El Akir. The Saracen's objective is to kidnap King Richard the Lion-Hearted, who it so happens is visiting the wood. While the Saracens fail in their mission, they do kidnap Barbara and an English noblemen, William des Preaux, who pretends to be Richard to protect the king. Meanwhile, The Doctor, Ian and Vicki rescue another English noblemen, William de Tornebu, and return with him to visit the King.
King Richard eventually decides to knight Ian as "Sir Ian of Jaffa", who is sent off as an emissary to Saladin, the leader of the Saracens. Ian is to offer the hand of his sister Joanna, in marraige to Saladin's brother Saphadin. In addition, Ian will try to rescue the kidnapped Barbara. Ian is waylaid on the way to visit Saladin by bandits, but eventually is able to trick the bandits and escape.
Barbara, however, is kidnapped a second time by El Akir and taken to his home. Barbara, however is rescued by a man named Haroun ed-Din, whose wife and daughter have been taken by El Akir. El Akir's soldiers search for the missing Barbara, and eventually recapture her. She escapes a second time, this time hiding in El Akir's harem with the help of Haroun's daughter Maimuna. El Akir eventually finds both Barbara and Maimuna and intends on killing them. However, Haroun finds them in the nick of time and kills El Akir. Haroun and Maimuna are joyfully reunited.
Barbara and Ian are then reunited and make their way back to the Tardis. Meanwhile, The Doctor and Vicki have been trying to survive the intrigues of King Richard's court. Joanna has informed her brother the King that she will not consent to marry Saphadin, which infuriates the King. The Doctor is eventually accused of being a spy and is sentenced to death. Ian, in disguise as "Sir Ian of Jaffa", rescues The Doctor under the pretense of being his executioner. The travelers then make their way back to the Tardis and resume their travels.
I haven't often mentioned guest stars in my reviews, but the duo of Julian Glover (the lead baddie in Indiana Jones and the Last Crusade) and Jean Marsh (Upstairs, Downstairs) are simply wonderful as King Richard and his sister Joanna. You can just feel the tension when Joanna tells the King that she refuses to marry Saladin's brother.
The Crusade is top-notch Doctor Who, and after the three less than stellar stories that preceded it, a real breath of fresh air.