A Winthrop House fire Saturday night filled the common room of an I-entry suite with smoke and prompted the Cambridge Fire Department to engage in an hour-long, unsuccessful search for the conflagration's source.

Two of the first-floor suite's three residents returned home at around 11:30 p.m. to find the smoke in their main room.

Anna-Lisa Espinoza '87 and Jill M. Ho-Tai '87 couldn't find the fire, however, and called a house security guard, who pulled a fire alarm signalling the Fire Department, said Mary P. Gallant '87, the third roomate.

Gallant returned to the room after a birthday party in her honor.

"A bunch of firemen standing in my room with axes is not my idea of a surprise party," she said.

It was originally thought that there might have been an electrical fire, but a search of the entryway yielded no results, according to University police.