Alexis might confront Beckett directly. She could say something like 'I think you're cheating on me. What's going on?' This is a very straightforward approach.
I don't know who Alexis is in this story without reading it. But it's likely that Alexis is either the main character or an important figure in the events that unfold in the 'creepy subway' setting.
As far as public knowledge goes, there is no clear indication of a love story between Krystle D'Souza and Karan Tacker. They might have a great on - screen chemistry which could be misconstrued as a romantic relationship off - screen. However, until they themselves come forward or there are reliable sources suggesting otherwise, we can't assume there is a love story.
A lawyer could be an important character. This lawyer takes on Alexis's case, believing in their innocence. The lawyer has to battle a corrupt legal system or powerful opponents who want to see Alexis locked up for good. The fanfic could show the lawyer's strategies and how they build a case in Alexis's favor.
Perhaps there have been some rumors or whispers in their fictional world that have reached Alexis' ears. Even if they are baseless, they can plant the seed of doubt in Alexis' mind, making her think that Kate is cheating.
She could be defensive of Beckett. Since Alexis probably has a good relationship with Beckett, she may try to convince Castle that he's wrong and that Beckett didn't mean any harm. For example, she might tell Castle about all the positive things Beckett has done for her.
Well, without more context, it's difficult to define Alexis' secret story. It might be related to a family secret that Alexis has been keeping. Maybe it has to do with an inheritance or a long - lost relative. Or perhaps it's a story about Alexis' first love that was full of unexpected twists and turns and they've chosen to keep it a secret.
Kate might get defensive right away. She could say things like 'How could you think that of me?' and be angry at Alexis for not trusting her. This is a common reaction when someone is wrongly accused in a fanfic or in real life.
Well, rumors often start from their on - screen pairings or their friendly interactions off - set. People might see them getting along well and assume there's something more. But these could just be normal friendships in the industry.
The Alexis Love Story might be a fictional one. Maybe Alexis is a character in a novel or a movie. In that case, it could involve a grand love affair set in a particular time and place. For example, if it's a historical setting, their love might be influenced by the social norms and events of that era. Or if it's a fantasy world, their love could have elements of magic and adventure.