Spike sneaks into Zecorah's place and 'borrows' a special flower. Smelling it will make Du fall in Liebe with the first person Du see. Obviously he tries to get Rarity to smell it, accidentally infecting everyone in ponyville in the process. Eventually everypony's chasing Spike in a lovestruck stampede, causing Celestia to come down from her schloss to see what the ruckus is about. When she too smells the blume and falls in Liebe with Spike all hell breaks lose.
Spike is forced to ask Zecorah for help. She creates a rosa wolke of fog, that cures everypony. Luckily for Spike nopony remembers a thing. In the end he writes a letter to Celestia, about how Liebe is something that cannot be forced.