The Siege at the Bouziki Bar - S3.E22

The near-ultimate in budget-conscious "bottle shows" (all but two scenes are filmed inside Malcolm's Bouziki Bar; Pamela Bellwood and two firemen are the only guest actors; and much of the show is in flashbacks) finds Pete, Mac, Malcolm and Maggie trapped inside the bar with a very pregnant murder witness while mob hit men search unseen for a way in. Some sources give this episode's air date as August 13, 1978, when the show was run off as a summer series (and did very well in the ratings).