One of the girls I lied to, seduced, and abandoned is trying to ruin my life.

How I Met Your Mother – The Final Four
Barney tries to find the mystery woman who is out to ruin his reputation, and he uses the basketball tournament-bracket to eliminate 64 suspects, all of whom have reasons to hate him.

During March Madness, Barney continuously strikes out when hitting on girls. He keeps getting slapped and he can’t figure out what’s going on. Later, he and Lily are at the bar and when he leaves the table an anonymous girl comes up and tells Lily that Barney will do whatever it take to get in her pants. Barney realizes that some girl from his past is trashing his reputation all over town, so he sets up a bracket to figure out which of the many, many girls it could be.

As the group goes through Barney’s scrapbook of girls he’s slept with, Lily says all the girls have a right to hate him. Robin stands up for Barney, saying any woman who sleeps with him knows what she’s getting into. The group turns the whole thing into a party, fighting over which girl gets to move on in the tournament, and we hear a terrific list of lies Barney has told in order to get girls into bed (you have my wife’s kidney, owner of Google, fake baby). At the end, they all feel sad and a little dirty. Except Barney, of course.

After they narrow it down to four girls, Barney and Lily track them down one by one, but Lily refuses to ID the girl unless Barney apologizes. Fantastically, two of the four girls are ones we have met in previous episodes. We see the girl Barney took to someone else’s apartment and then left her there to get arrested for trespassing, and we see the girl Barney met the night he pretended to be “Ted Mosby, architect.” Unfortunately, none of the girls is the girl.

The group sets up a sting, with Barney pretending to hit on Robin. When Barney “goes to the bathroom” a girl approaches Robin, but Barney doesn’t recognize her. Surprisingly, Barney is shocked that he could not recognize someone he slept with and he actually apologizes, but it turns the girl is just a friend of Robin's from work. And then Ted’s voiceover says, “Eventually Barney did figure out who the girl was, but more on that later.” Could it be the mother?

The ep ends with Barney typing up his blog in a nod to Doogie Howser, M.D. It's really not that clever. It's only like 20% funny … and 80% lame.