A detective tries to prevent the assassination of President-elect Abraham Lincoln during a train ride headed for Washington in 1861.

Ellen McNulty leaves her New Jersey hamburger stand and heads west to pay a surprise visit to her son and his new bride. When Ellen arrives, her daughter-in-law mistakes her for the maid she has hired for a big party they are throwing. Rather than cause any embarrassment, Ellen goes along with the charade, which leads to many complications.