lose the plot

verb loses the plot · losing the plot · lost the plot

1. UK, colloquial, idiomatic To cease to behave in a consistent or rational manner. I lost the plot for a while then. And I lost the subplot, the script, the soundtrack, the intermission, my popcorn, the credits and the exit sign.
2. UK, colloquial, idiomatic To lose sight of an important objective or principle; to act contrarily to one's own interests through concentrating on relatively unimportant matters. But while there remains a considerable degree of consensus that the consequence of apparently losing the plot sometime between 1914 and 1918 was the cultural and economic malaise of the 1920s and 1930s, there are still some who look back on the interwar years less with criticism than with nostalgia.
3. Used other than figuratively or idiomatically: see lose, plot. Readers enter the storyworlds of novels and then follow the logic of the events that occur in them primarily by attempting to reconstruct the fictional minds of the characters in that storyworld. Otherwise, readers lose the plot.