Most who have seen, or even heard of, Downton Abbey probably think of it as a mannered period drama and not a mystery. The series did capture an era of rapid change at the beginning of the 20th century -- down to the place settings and livery -- but it also thrived on intrigue. Many of those plots not only added to the drama, but propelled whole seasons of the plot forward. One the series' most tantalizing mysteries, however, was never fully resolved, and it's related to the incident that began the entire show.
Source：https://www.cbr.com/downton-abbey-greatest-mystery-patrick-survive-titanic/
