It's the year 2030 and an older Ted Mosby is telling the story to his son and daughter about how he met and will eventually marry their mother. This is where we meet for the first time Ted, Lily, Marshall, Barney and Robin.
Marshall and Lily enter a Halloween costume party and Robin brings her new boyfriend. Ted and Barney go to the same Halloween party they go to every year where Ted looks for his lost love, the Slutty Pumpkin.
It's New Year's Eve 2005 and Ted spends a large portion of his Christmas bonus for a limo for he and the gang. In addition, he has outlined a plan how they will ring in the New Year. Unfoirtunatley, things don't always go as planned.