Kat is a recurring character on 90210, portrayed by Tiffany Hines.
Kat is a detective that worked with Navid Shirazi to arrest his Uncle Amal, who was running a car theft ring and framing Navid for it. Navid approached her after Amal threatened to harm Silver if he didn't keep his crimes quiet.
Kat later went to Las Vegas after Navid was given a package to deliver to one of Amal's associates there. While she was putting a microphone on him, Silver walked into the room. Kat kissed Navid to cover for the fact that they were preparing a sting, causing Silver to believe that Navid had moved on.
Kat continues to work with Navid, but when his wire is discovered, he is assaulted and given a warning. Afterwards, Navid calls Kat to his house and prepares to find evidence on Amal, but comes across a gun and thinks about using it. Kat, seeing this as serious, goes to see Silver and asks her to talk to him so that he won't get himself hurt.
In the end, Omar Shirazi returns from Iran and turns himself in for past crimes, offering information on Amal to the police so that Navid would not have be involved.