John and Mary appeared in “The Blind Fortune Teller” in Season 1.
Interestingly, the episode did not reveal that Mary already had a bun in the oven, so either Sean Pertwee knows something that the show didn’t give away in Season 1 or he’s going with the assumption that baby Robin was going to be born sooner rather than later.
As the episode also happened to feature the introduction of Jerome, their debuts were rather overshadowed, but they ended the episode happily engaged and ready for a life together that definitely wasn’t going to end with them both plummeting to their deaths in front of their son.