Who sabotaged Maddie's skates in Kiss Me, Captain?

On competition day, Emily is sitting in the stands with her mother when she hears two girls from another team whisper that someone loosened Maddie's skates. Emily believes them and runs for the ice to warn her, but security won't let her through mid-performance. Maddie goes for her triple axel, loses the blade's grip, lands badly and doesn't get up.

Later, Maddie tells detectives that her blades felt looser than usual when she put them on, as if the mounting screws hadn't been tightened all the way. She had felt something was wrong before she ever stepped on the ice.

Detectives Sarah Cranes and Michael Rodriguez question Maddie in her hospital room. Security footage shows someone entering the locker room about twenty minutes before her routine. Maddie names Jenna Caldwell, Carol Martinez and Sophie Chen, the three skaters cut from the team, and blames jealousy over the captaincy for the conflict. She keeps the deeper reasons vague.

Emily then admits she overheard girls behind her mocking Maddie's equipment and calling her the ice queen during the routine. She had kept quiet before this because reporting it would have exposed the bullying, Maddie's invented background and the rumors that they were too close.

Two weeks after Maddie's surgery, Madeline Foster tells her that Carol Martinez has confessed to tampering with the skates. Three girls face criminal charges, and the investigation is closed. At the university hearing in chapter 57, the panel expels Jenna, Carol and Sophie and refers the case to local police. On her way out, Jenna warns Maddie that things are about to get worse for her.

The book doesn't say whether the person on the footage was Carol herself, or exactly how the work was split among the three. What it does make clear is that Carol was the one who confessed, as part of a group that had targeted both girls for months.

The sabotage didn't come out of nowhere. Emily had already accused the same circle of loosening her blade guards. Jenna, Carol and Sophie later attacked her in the showers, and Coach Marquette pulled them from the Nationals roster. The skates were the most dangerous step yet in a long campaign.

It also cost Maddie her season. She needs ankle surgery and months of recovery, and the investigation keeps threatening to drag out the secrets she has guarded hardest. That's why who did it matters so much to her story.