Well, in a fanfiction where Tess is kidnapped, it could lead to all sorts of plot twists. The kidnappers might be from a rival group that wants to use Tess as leverage against Joel and his group. Joel would be forced to make some difficult decisions. He could try to negotiate with the kidnappers, but knowing him, he'd probably prefer a more direct approach like a rescue mission. Ellie might also be in danger if the kidnappers find out about her importance. It would be a very tense and action - packed scenario.
Joel could use his combat skills and stealth to infiltrate the place where Tess is being held. He'd probably take out the guards one by one and then free Tess.
A possible plot is that they discover a hidden community that seems too good to be true. They have to decide whether to trust it or not. Joel is skeptical while Tess is more open - this could lead to some internal conflict between them. Also, a story about them finding a lost child and having to decide what to do with it would be interesting. Tess might want to help the child while Joel is more worried about the risks it brings.
One way is to show their softer sides with each other. In the game, they are tough survivors, but in fanfiction, we can explore moments where they comfort each other. For example, after a near - death experience, Joel could hold Tess and tell her how important she is to him. Another way is to introduce external factors that force them to rely more on each other. Maybe a new and more dangerous type of infected appears that they have to figure out how to deal with together.
The last place in a Tess Monaghan novel could be anywhere depending on how the plot unfolds. It might be a seedy bar where she finally confronts the villain. Or it could be a park where she has a crucial conversation that ties up all the loose ends of the story. Without knowing the specific novel, it's hard to pinpoint exactly.