Melissa Armstrong

Melissa Armstrong (born June 9, 1984), formerly known as Amber Vitale, is a young woman from New York and the ex-girlfriend of Detective Danny Williams.

Early life
It is revealed In Season 5 episode, Nanahu, Amber reveals her past - she was born Melissa Armstrong, and in her own words, "didn't have much of a family as a kid".

At age 19, she met her future husband, Frank Simpson, as he was older and charming, and the first man who made her feel special. She married him a year later. However, Frank became too controlling, and when she stood up for herself, he began being abusive, which landed her in the hospital twice.

In 2013, after Frank again nearly killed her following an argument, Melissa Armstrong-Simpson filed a complaint to NYPD, and Frank was arrested on felony charges, while Melissa, obtaining a restraining order against him, flew to Hawaii and changed her name to Amber Vitale.

Meeting Danny
In O kela me keia manawa Melissa meets Danny Williams at a gas station where she asks him the way. She tells him that she’s new on Hawaii and wants to start over there. When she is shot in an accident, Danny calls an ambulance and starts looking for the shooter. After ‘solving the case’ he visits Amber in the hospital and introduces himself to her properly. Melissa gives him her fake name, Amber Vitale.

In "Ku I Ka Pili Koko" Melissa spends the night at Danny’s place where she meets his daughter Grace for the first time. Steve mentions that Danny has been spending a lot of time with Melissa, implying they have been an item for some time already. However, Danny is afraid of committing to the relationship. When Danny and Steve are trapped in a building after an explosion, Melissa is genuinely worried about Danny and introduces herself to Kono as his girlfriend. Eventually, Steve convinces Danny to give the relationship a try.

In "Nanahu", Melissa's husband, Frank, returns to Hawaii to win her back. He looks for Melissa at Kamekona’s shrimp truck, leading a suspicious Kamekona to call Five-0 and give his license plate number. A background check reveals Melissa’s past to the team. Meanwhile, Danny and Melissa take a romantic getaway. Frank follows them and stabs Danny, before Melissa runs over him with Danny's Camaro, effectively killing him.

In Lupao’i, as Danny and Melissa are waking up, the phone rings. Melissa asks Danny what's wrong to which he replies with "work". Danny goes to shower when he receives more messages; Melissa looks over at the phone and sees that Danny lied and the texts were from Rachel. It is later revealed that Rachel needed Danny’s help as their son Charlie was suffering from a rare illness. However, Danny doesn’t tell Melissa the truth about this.