Iron Man: First Mission

Book 3 in The Guard and The Prince series.

After the events of New York and after her visit to Asgard, Nyx returned to Earth. However, not by herself. She brought Loki back with her and became his watcher. She didn't go back to work for SHIELD. She couldn't after losing Phil. So she kept Loki safe and in turn protected the world from Loki. She kept in touch with the Avenger's however no one knew why she quit working for SHIELD. She planned to keep it quiet until the news of Tony's death reached her.

Now it was time for her to come back. Only Nyx knows she can't do it alone. She turns to Loki because she wants to give him a chance, but she also fears how the other Avengers will react once they know that she has been harboring the person who destroyed New York. However, she will risk anything to help Tony and give Loki a chance at proving himself to be the man she knows he is.