One of How I Met Your Mother's mysteries is about to be revealed.
Smulders joked that she was terrified of Lithgow after his Emmy-winning role as a serial killer on Dexter, but added, "It's really exciting and different for our show. He's such a pioneer."
Barney (Neil Patrick Harris) previously believed his dad was Bob Barker, apparently a lie told by his promiscuous mother, who's portrayed by Frances Conroy. Megan Mullally provides the character's voice in flashbacks.
The episode will air at the end of February. How I Met Your Mother airs Mondays at 8/7c on CBS.