How dare you, Lily?!?

On this Monday's episode of How I Met Your Mother, Marshall's better half will do something so dastardly and unfair to her husband that we can't even print it here.

Elsewhere, with Ted settled in to his new apartment, Barney will decide the pair should go out every night; while Robin hits a high point in her career.

Watch the following promo to see what Lily actually does and then, as always, return to TV Fanatic soon after the episode airs for an updated section of How I Met Your Mother quotes...

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.