lose the 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.

Right then I lost the plot. I did, man, I went over the edge.

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.