6. And Those We've Left Behind

Complete story — includes the ending

All over Boston, time anomalies are occurring, looping back four years. The Fringe team traces the anomalies back to a married couple. The husband has used his wife's research to construct a machine that reverts their home to the state four years prior, before she fully suffered from rapid deterioration of Alzheimer's disease. He has been convincing her younger version to complete her research to allow him to stabilize the time bubble. With help from Walter, Peter enters the house, and he and the wife persuade the husband to shut down the machine, which is later disassembled by the FBI. The husband intends to rebuild it later, but he discovers that his wife has blacked out all the equations she had written down. In the end, Peter notes that the husband's success with the time bubble started simultaneously with his appearance in the alternate timeline.