"P. S. I Love You" -- Barney uncovers the lost episode of Robin’s (Cobie Smulders) "Underneath the Tunes," as Robin Sparkles, on HOW I MET YOUR MOTHER, Monday, Feb. 4 (8:00-8:30 PM, ET/PT) on the CBS Television Network. Photo: Cliff Lipson/CBS © 2013 CBS Broadcasting, Inc. All Rights Reserved.

"P. S. I Love You" -- Barney (Neil Patrick Harris, left) uncovers the lost episode of Robin’s "Underneath the Tunes," as Robin Sparkles, on HOW I MET YOUR MOTHER, Monday, Feb. 4 (8:00-8:30 PM, ET/PT) on the CBS Television Network. Also pictured: James Van Der Beek (right) guest Stars as Robin’s Ex-Boyfriend Simon Photo: Cliff Lipson/CBS © 2013 CBS Broadcasting, Inc. All Rights Reserved.

"P. S. I Love You" -- Barney uncovers the lost episode of Robin’s "Underneath the Tunes," as Robin Sparkles, on HOW I MET YOUR MOTHER, Monday, Feb. 4 (8:00-8:30 PM, ET/PT) on the CBS Television Network. Pictured: Alex Trebek guest Stars as himself Photo: Cliff Lipson/CBS © 2013 CBS Broadcasting, Inc. All Rights Reserved.

"P. S. I Love You" -- Barney uncovers the lost episode of Robin’s "Underneath the Tunes," as Robin Sparkles, on HOW I MET YOUR MOTHER, Monday, Feb. 4 (8:00-8:30 PM, ET/PT) on the CBS Television Network. Pictured: Jason Priestley guest Stars as himself Photo: Cliff Lipson/CBS © 2013 CBS Broadcasting, Inc. All Rights Reserved.

"P. S. I Love You" -- Barney uncovers the lost episode of Robin’s "Underneath the Tunes," as Robin Sparkles, on HOW I MET YOUR MOTHER, Monday, Feb. 4 (8:00-8:30 PM, ET/PT) on the CBS Television Network. Pictured: Luc Robataille guest Stars as himself Photo: Cliff Lipson/CBS © 2013 CBS Broadcasting, Inc. All Rights Reserved.

"P. S. I Love You" -- Barney uncovers the lost episode of Robin’s (Cobie Smulders) "Underneath the Tunes," as Robin Sparkles, on HOW I MET YOUR MOTHER, Monday, Feb. 4 (8:00-8:30 PM, ET/PT) on the CBS Television Network. Photo: Michael Yarish/CBS © 2013 CBS Broadcasting, Inc. All Rights Reserved.