Ariana Kane was The Alliance's head of Counter-Intelligence. She was sent into SD-6 in order to investigate the "murder" of Emily Sloane after it was revealed that an unknown third party had interfered with Arvin Sloane's attempt to poison her, as well as the subsequent blackmailing of Sloane after SD-6's internal attempts to discover the perpetrator were unsuccessful.
As Head of Counter-Intelligence
Requesting her personally to SD-6 to investigate the situation surrounding Arvin Sloane, Ariana Kane immediately launched a witch hunt specifically focused on Jack Bristow, claiming that his responses were too perfect, adding that "... I mean, he even gets angry when it makes strategic sense." (The Abduction) Kane believed that he had the perfect motive to blackmail Sloane. Suspecting many of Jack's missions to be misleading, she launched an investigation leading to the questioning of Jack regarding the death of CIA agent Steven Haladki, as they found his DNA on a gun Jack used from the armory (A Higher Echelon). All of this prompted Jack, with the help of the CIA, to fabricate security footage and physical evidence to "prove" that he had indeed been in the locations stated and eliminating all suspicions of his work as a double-agent with the CIA. This evidence passed Ariana's scrutiny, but she was not satisfied. Ariana requested Jack's SIM card to verify phone calls and cell-tower information to more accurately determine whether the information Jack had supplied was accurate. Michael Vaughn and the CIA attempted to help Jack by sending an agent posing as a waiter to take Jack's phone, creating a dummy SIM card to fool Kane. The attempt ultimately failed as the ink had not dried on the dummy SIM card, causing a stain on Kane's hands and veryifying her suspicions. She quickly ordered her agents to capture Jack. He went into hiding with the CIA with a solution pending.
Sydney Bristow's cover was nearly blown while having dinner with Vaughn. Ariana's agents identified Vaughn leaving the airport with Sydney and discovered that he worked for the CIA by hacking into the DMV database. Vaughn and Sydney neutralized the agents, and Ariana never discovered Sydney's affiliation with the CIA.
Whilst Jack was hiding out with the CIA, he recognized that the only way for him to clear his name was to discover the identity of the true perpetrator. He took the information he had obtained to Irina Derevko, a prisoner of the CIA, with them both reaching the conclusion that it was actually Ariana herself behind the blackmailing of Sloane after Jack retrieved security tape footage showing Jean Briault, who Arvin Sloane had previously murdered, and Kane in a hotel in Lima, Peru, implying their affair. This gave her a motive for blackmail: revenge. Although Kane's accounts are shown empty, it is later discovered that she deposited the bearer bonds only long enough that she could convert it into cash, clearing Jack's name.
When Jack returns to Irina, she suggests that Sloane requested Kane personally as he knew she would be easy to frame. (The Getaway)
Quotes
"Men always call women crazy when they're caught with their pants down." (The Abduction)
"His answers are too perfect. I mean, he even gets angry when it makes strategic sense." to Arvin Sloane (The Abduction)
"Yes, I read your report. I think either she was an accomplice to his blackmail or else the two of them have been up to something more long-term. You must have noticed that Bristow frequently assigns his daughter to operations of his own design." to Arvin Sloane regarding Sydney and Jack Bristow (The Getaway)