Nick Cave penned the script and co-wrote the soundtrack with Warren Ellis for this John Hillcoate-directed tale of outlaws facing death — and “The Proposition” of life spared if one brother will murder the other — in the Australian outback of the 1880s. With death spooking every move, Cave adds muted vocals that serve as sermons of deep intent to “Down to the Valley” and “Gun Thing.” But this is mostly an ominous and tense collection of instrumental pieces highlighted by the torment of Warren Ellis’ string arrangements that slowly bleed throughout. It plays as a Western through the ears of a horror film score. “Martha’s Dream” has a windy fatality haunting its notes. “Moan Thing” ensnares a modern ethereal blues with a variety of odd sounds poking out. “Happy Land” is only “happy” in the sense that it’s a sublime, gentle instrumental piece in the midst of other pieces where violence is a shot away. “Sad Violin Thing” delivers on its title’s promise.