In Twinless, two grieving young men form an unlikely friendship through a support group for people who have suffered the death of their twin. Roman (Dylan O'Brien) and Dennis (James Sweeney) both search for solace and an identity without their siblings and soon become inseparable outside the group. But when Roman meets Dennis's ebullient co-worker, Marcie (Aisling Franciosi), viewers discover that all is not what it seems, as each man harbors secrets that could unravel everything.