“There are 23,000 nuclear weapons in the world,” the film announces, “and we don’t know where they are.”

British filmmaker Lucy Walker’s “Countdown to Zero” (Magnolia Pictures) is a sober but captivating investigation into the dangers of nuclear weapons, exposing a variety of present-day threats and featuring insights from a host of international experts and world leaders who advocate total global disarmament.

One of the highlights of the documentary is the testimony of Valerie Plame Wilson, former CIA agent and ambassador Joe Wilson’s spouse (re “Plamegate”).

Nuclear weapons have proliferated to nine nations and that number could continue to grow, we’re told, as over forty nations have the technical capacity to construct nuclear weapons. Terrorists are actively seeking nuclear weapons and fissile material–not to be used as political leverage, but rather as tools of mass destruction. But what is just as worrisome is the threat of human error; the possibility of an accident increases every day.

Written and directed by Walker and produced by Lawrence Bender (has produced several Quentin Tarantino movies).