- Previous episode S12E11 - The Paintball Scattering
- Number S12E12
- Director Mark Cendrowski
- Writers Chuck Lorre, Jeremy Howe, Maria Ferrari, Dave Goetsch, Steve Holland, Eric Kaplan
The Propagation Proposition
Penny's ex-boyfriend, Zack, and his wife want a baby, but when Zack is infertile, they ask Leonard for help. Also, Koothrappali attempts to mend things with his ex-fiancée, Anu.