Michelle is the wife of Sam Hanna and the mother of his children. She is a CIA Agent who has returned to work after caring for her family for an unknown period of time. She met Sam eight years ago while they were working on a mission at the task force.
She did not resign even if she put her career on hold. She returns to work when her cover Quinn is the only one capable of approaching Isaak Sidorov who put his hands on nuclear bombs. The case is on hold, but allowed Michelle to realize that she still loves her job, to the point of not wanting to be sure to take her place as a mother and wife when everything is finished. Sam is very concerned about the situation.
Near the end of Episode: Descent she was pushed out of a high building and left hanging during a fight with the Russian girls. During an undercover operation she and her husband were sent in in order to foil Isaak Sidorov's plan and capture him. As Kensi Blye arrived at the scene, Michelle dangled from a balcony, but managed to free herself and help Kensi against the Russian girls.
She then learns Sidorov's location from one of the girls and confronts Sidorov and tells him that the two girls he sent after her are dead.
Sidorov then tests her loyalty by having her shoot Sam and Deeks, supposedly killing them, but in fact only injuring them.
She then continues her undercover duty in order to find out where the nuclear bombs are, by getting in league with Sidorov and going with Sidorov, and his men to set up a deal, relating to the nuclear bombs.
She continues pretending to be in love with Sidorov, during which she texts NCIS vital information about the nukes, almost being caught by Sidorov, and having to kiss him after wards.
Eventually, NCIS determines that Sidorov and his men have never left the Cambridge hotel, where they were staying, and were going to make a secret escape, But NCIS confronts them on the helipad, during which Sidorov takes her hostage and declares his love for Quinn is weakness, but Sam denies and she witnesses Sam shoot him dead numerous times. Later NCIS was able to retrieve the stolen nukes.