Fire crews were called to a blaze in Chapel View Flats in Chapel Street yesterday.
There was a fire in a second floor flat in the living room area of the home.
Two fire engines from Luton and one from Stopsley were called to the flats at 10.43am.
One male casualty was treated at the scene by paramedics for smoke inhalation.
Scenes of crime officers and fire investigation officers remained in the building throughout the afternoon to establish the cause of the blaze.