When Marshall picks up smoking again, it prompts Lily, Ted and Barney, ex-smokers all, to succumb as well. Meanwhile, Robin gets a new co-anchor at her show...
When a perfect girl finally shows up, the gang tries everything to help Ted, while Marshall takes action when he discovers a letter written by younger himself.
After Barney (Neil Patrick Harris) and Robin hit a rough patch in their relationship, Lily devises the perfect plan to break them up, calling in help from Robin's famous friend, Alan Thicke.
