The novel opens with an account of a lost child in 2113 and then moves forward to the year 2135. The Chairman of the Arts Department informs Joseph Dashper, a lecturer at Camford University, England, that his bid for a new department is not going to be funded.
Joseph also discovers that his chairman's daughter, Alice, is keen to start a relationship with Joseph. The world is in the grip of a population decline and Joseph rejects Alice's offer.
Joseph agrees to let his friends, Ralph and Eric, perform a physics experiment in a storage shed at Monksbridge Hall, his family property. The experiment opens up a portal to the year 1535 as an unexpected side effect. Eric becomes ill with the plague. Joseph is persuaded to make a crossing in the hope of retrieving artifacts.
Sister Miriam is initiated into a religious order in 1523. After her move into a new cell she begins to have visions. She later has an unfortunate encounter with a young monk. The story of Miriam progresses to the year 1535 when the librarian suffers a compound fracture of his leg and Miriam is placed in charge of the library. The Abbot threatens to close the library. Miriam has fresh visions which are troubling.
Joseph meets Miriam on a crossing and she helps him obtain records from the library. He returns for more records but finds Miriam dying from the plague. He brings her temporarily to his own time and nurses her back to health. Joseph later removes all the records and books but leaves behind a 'Jeweled Bible'. Miriam was to return with him to 2135 but remains to visit her dying father.
Joseph is unable to return for Miriam because the portal is closed. Miriam helps to heal the librarian's leg but runs foul of the Abbot because of her faith healing. The loss of the books is discovered and Miriam is accused of sacrilege. She is tried before the Bishop and found guilty. She is to be transported to Salisbury for sentencing by the civil authorities. The end of the trial is interrupted by a thunder storm
The story moves rapidly as the peasants revolt against the Abbey. Ralph and Eric get involved with the destruction of the Abbey with fatal results.