When the world turns spooky, there are worse places to be than a citadel (or, in Arabic, a casbah). Tonight, this particular fortress just so happens to be filled with costumed tricksters and a lineup of musical treats. Justin Robinson & the Mary Annettes headline the bash with their twisted folk-pop curios. Also playing are Andrea and Pete Connolly of Birds and Arrows, and string-band gents Corn & the Colonels. The 9 p.m. show is all-ages; tickets are $8, or $5 for those in costume. —Ashley Melzer