The Acton Memorial Library will present “Acton’s Unsinkable Mrs. Brown: ‘Titanic’ Survivor Carolyn Lamson Brown” at 7 p.m. Tuesday. Local historian and Acton Memorial Library trustee Dennis Ahern will tell the story of Caroline Lamson Brown, widow of J. Murray Brown of Acton and Belmont, and how she came to be the last person to step off the doomed ship’s deck into a lifeboat. Caroline Lamson Brown became a trustee of the Acton Memorial Library in 1918 and served on its board until her death in 1928. This month marks the 100th anniversary of the Titanic’s lone voyage. The program is sponsored by the Acton Memorial Library Foundation.