Dr. Besson treated Paul Raines, who was shot by Dave Conlon. Besson told Audrey Raines that Paul might not be able to use his legs anymore. Later on, Paul experienced further complications and had to go back into surgery, but Jack Bauer and Curtis Manning brought in Lee Jong and forced Dr. Besson to save him instead. Already in critical condition, Paul died as a result. The doctor was present when Jack and Melissa Raab questioned Lee concerning the whereabouts of Habib Marwan.
On Day 5, Dr. Besson was assigned to Tony Almeida as he recovered from injuries sustained in the car bombing that claimed the life of Michelle Dessler. Besson suggested to Bill Buchanan that Tony should not find out about Michelle's death, as it would interfere with his recovery.
Besson was in the medical wing during the nerve gas attack, and saw Christopher Henderson into the area. Besson survived the attack, but was knocked out by Tony, who intended to kill Henderson.