Ricci told Entertainment Weekly that the assassination of President Kennedy will have a big impact on Maggie.
"In the next couple of episodes, Maggie does get involved in some very shocking and illicit behaviour," she said.
"She doesn't take the death of JFK very well and it sort of propels her to a very dark area... She's still going to be fun, but she's going to be spinning a little bit and make some very bad choices. Which is entertaining for everyone!"
Ricci also revealed that she is still unsure about Pan Am's future despite rumours last year that it had been cancelled.
Urging fans to keep tuning in and write messages on the ABC website, Ricci said: "Just like any other show waiting to see if they're being picked up for a second season, we'll find out in May if we're going to be coming back for a second season."
Meanwhile, ABC president Paul Lee told reporters at the Television Critics Association press tour that the future of Pan Am is still up in the air, Entertainment Weekly says.
"When it opened, it really brought an audience," he said. "There's such a feeling of goodwill toward that show. We have new and original shows right through February."
Pan Am airs on Sundays at 10/9c on ABC.
> Pan Am: 'Secrets and Lies' recap
> Pan Am: Why we'd like a second season