On Thursday, 1 December 1955, in Montgomery, Alabama, civil rights activist Rosa Parks refused to give up her seat, on a segregated bus, to a white passenger, when the bus became crowded enough that she was required to move. Parks was arrested, leading to the Montgomery Bus Boycott, beginning on 5 December, and, ultimately, the end of racial segregation in America.
Krasko's attempts to alter this crucial event in history were thwarted by the Thirteenth Doctor and her companions, Ryan, Yasmin, and Graham. All four were present on the bus when Rosa Parks took her stand. (TV: Rosa)