Lose the plot

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.

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

Finally, I lost the plot. I got into my car and drove to the police station.

Apologise for losing the plot and explain what made you react the way you did.

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.

Because of this it seems to me that we have somehow lost the plot and we're in desperate need of balance. The idea of Protestant ministers touching the body of Christ (the bread) with great love and tenderness like the priest described is almost incomprehensible.

2011, House of Lords Select Committee on Economic Affairs, 2nd Report of Session 2010-11: Auditors: Market Concentration and Their Role, Volume II: Evidence, page 19, [Professor Fearnley:] If I can perhaps be a little unkind about my profession — which is fair enough I suppose — I think the accountancy profession, along with other professions, loses the plot from time to time and has to be pulled back from what it was doing before.

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.