本季故事从罗宾(寇碧·史莫德斯 Cobie Smulders 饰)和巴尼(尼尔·帕特里克·哈里斯 Neil Patrick Harris 饰)的婚礼说起。 时间回到2012的夏天,这是个充满爱的季节。巴尼和女友奎因,泰德(乔什·拉德诺 Josh Radnor 饰)和女友维多利亚,罗宾和男友尼克,以及马修(杰森·席格尔 Jason Segel 饰)、莉莉(艾丽森·汉妮根 Alyson Hannigan 饰)和儿子一家三口,每个人都非常幸福。马修夫妇忙于照料孩子,其他三对情侣和和美美。然而10月份一到,他们就迎来了传说中的“分手季”。经过一番折腾,巴尼和奎因分手了。不久后,泰德和维多利亚也因为一个不可调和的原因分手了。随后,巴尼宣布和罗宾订婚,这究竟什么怎么一回事……As Ted and Victoria are about to run off together, Ted convinces Victoria that she needs to leave a note for her fiancé Klaus to give him some closure on the situation. But leaving that note is not as easy as Victoria going back to the church. Ultimately to help Victoria, Ted may have to overcome a childhood phobia. Meanwhile, Quinn, who does not have a lot of what she considers close girl friends, asks Robin and Lily to stand up for her when she and Barney get married. This request brings up the fact that Quinn has no idea that Robin and Barney used to date, which Barney has no intention of ever telling her. In fact, Barney has managed to erase all history of his and Robin's romantic past. Sleep deprived new parents Marshall and Lily, and some deep seated beliefs of Klaus' will directly and indirectly affect what happens between both Ted and Victoria, and between Barney and Quinn.