It's seventeen hours before the wedding and Marshall begins to deliver another slap to Barney. We flash back to when Marshall announced his plan for this latest slap. Marshall spills something on his already soiled suit. Barney refers to Marshall's attire as a slap in the face of suits everywhere and that is what starts Marshall of on his tale. Marshall tries to scare Barney by claiming to have been taught by three masters of slap. Robin, Lily and Ted each play one of masters sought out by Marshall in hopes of unlocking the three secrets to delivering the best slap ever.