"Hawaii Five-0" said goodbye to a major character on the season finale of the fourth season. 

On the season finale of the series, Five-0 revisits Catherine's (Michelle Borth) past. During a charity poker night, she receives an unexpected phone call from Amir, an Afghani father she met during her tour of duty eight years prior. 

A flashback shows that Rollins saved Amir's son from going into a land-mine filled field to get a soccer ball. 

Amir remembered the kind gesture when he found Catherine wounded in the field a year later. He snuck her into his home and tended to her injuries. He even hid her in a secret tunnel when the Taliban came to look around. 

The call in the present day alerts Catherine that his son, Najib, has been taken by the Taliban, who will most likely be used as a human bomb. 

She and McGarrett (Alex O'Loughlin) then go to Afghanistan, where they find a wounded Amir, but Najib is nowhere to be found. 

They are later able to intercept a Taliban convoy that is transporting children. While they're saving the children, Steve is knocked off by a grenade blast, and is taken away by the Taliban. 

Before the Taliban can begin torturing him, the U.S. army comes in and saves him. 

The CIA and military, who are equally angry about the situation, force McGarrett to go back home. Before he goes, he gets a call from Catherine, who says she is staying behind to find Najib, who has been taken across the border. 

The episode wraps up Season 4, and leaves Catherine open to return in the future. But for now, Michelle Borth has exited the series, meaning McGarrett may find a new love interest next season.