The movie is set in Beirut and centers around a group of men coming to term's with their friend's drowning. His funeral becomes a "a heartfelt farewell not only to their beloved friend, but to the beauty and sensuality of life, youth, friendship, and love". In Islamic tradition drowning is a form of martyrdom (hence the title). The film has been making waves at SXSW while it was also nominated for the Queer Lion award at last year's Venice Film Festival.
Source 1: https://www.youtube.com/watch?v=6rwI_vwyzjg
Source 2: https://www.queerty.com/watch-new-film-martyr-explores-masculinity-homoeroticism-islam-intersect-20180314