In the first book, Ian is first seen talking to a preast at Grace Cahill's funeral along side Natalie. The two of them choose to accept the hunt for the 39 clues instead of taking a million dollars each. Later, Ian and Natalie are seen talking to Irina Spasky about where to find the next clue. They attack Amy and Dan with a poison needle gun in The Catacombs, attempting to leave them down there forever. They reveal that they were the ones who ordered Amy and Dan to be cemented underground. Amy and Dan are rescued by Alistair Oh. Later, Ian steals a secret formula from Amy and Dan.
In the second book, Ian and Natalie drag Amy and Dan onboard their yacht after sinking their boat. They search Amy and Dan to see if they have anything of value. After concluding that they don't, Ian and Natalie have the other two thrown overboard.
Their next appearance is in book 3, when they steal Amy and Dan's passports and kidnap Nellie. They are seen on the plane trying to put poison in Nellie's drink. Later, Natalie and Ian form an allience with Amy, Dan, and Alistair. It is revealed that Ian secretly has a crush on Amy, and Amy returns these feelings. They go to a cave in South Korea, Ian and Amy kiss briefly, dance when they find the clue, but then Ian and Natalie leave Amy, Dan, and Alistair in the cave.
In book five, Ian and Natalie meet Amy and Dan at the airport. Ian attempts to flirt with Amy, but Amy steps on his foot and runs. Later, Amy receives a phone call from Ian, who tells her that the next clue has already been found. Amy accuses him of lying.
In the sixth book, Ian and Natalie's mother, Isabel, joins the hunt. Ian calls Amy on the phone and tells her to meet him. When Amy arrives, Ian appears in a boat along with Isabel. They take Amy to a cave, and Isabel asks to form an alliance with Amy and Dan. When Amy refuses, Isabel orders Ian to throw dead fish into the water to attract sharks that will kill Amy. Later, the Kabras and Irina Spasky drop poisonous animals on top of the Cahills. Ian and Natalie are last seen being knocked out by Irina.
In the seventh book, Ian, Natalie, and Isabel tie Amy, Dan, and Nellie to chairs and try to cut them up in a jet engine.
In book 8, Ian and Natalie kidnap Dan, knock him unconscious, and place him on a conveyer belt in a toy factory. Later, Ian tries to steal a secret formula from Amy and Dan, but he ends up almost falling down a mountain. Amy has a choice. She can either grab the formula and leave Ian to die, or she can save Ian and let the formula fall to the ground. She chooses Ian's life over the formula.
In book 9, Ian, Natalie, and Isabel chase Amy and Dan through a park. Amy and Dan split up, and Isabel orders Ian to follow Dan while she and Natalie ran after Amy. Ian is caught in a trap set by Dan.
In the tenth book, the Kabras are seen fighting over the clue at The Globe Theater. Later, Ian is seen breaking into the forbidden wing in his family house to discover what his parents were hiding from him. He discovers that his mother was responsible for the deaths of Amy and Dan's parents. As a result, he and Natalie trick there mother into getting on the wrong plane. They enter the gauntlet with the rest of the Cahills. When they finally reach the end of the gauntlet, they meet Isabel, who makes it perfectly clear that she doesn't care about them. Ian refuses to obay his mother telling her "I'm not your servent, I don't even want to be your son anymore." Isabel disowns him, and he tells her he doesn't care. After Isabel is given a memory erasing pill, Ian says that when she regains consciousness, he's going to disown her. He gives Amy and Dan his clues, not trusting himself because of his lust for power.