Very freely adapted from Upton Sinclair’s meatpacking expose The Jungle, Tantalus Theatre Group’s ambitious two-hour rock opera/bar act delivers a strong score and dedicated performances. The company transforms Sinclair’s muckraking depiction of the Chicago stockyards circa 1905 into a brutal but maddeningly indeterminate portrait of a “music plant.” Wannabe star Jurgis, an immigrant as in Sinclair’s book, pursues his dream and loses his way, his wife, and his family. Finally he achieves a perverse peace by surrendering to the status quo of the music-making machine. Ed Plough’s songs, well performed by the tenacious ensemble, unleash a ton of eloquent anger and end with a lovely lament. Though this adaptation is too abstract, never arriving at specific parallels for the abuses Sinclair detailed, its progressive spirit rings as true as Sinclair’s did 100 years ago. Through 8/30: Mon-Tue 8 PM. Joy-Blue Club, 3998 N. Southport, 773-960-2066. $10.