The idea of artists overcoming adversity is a modern theme du jour, with dreary storylines custom-made for television documentaries. Yet it's hard to imagine any comeback more unlikely than the one achieved by Steve Earle, who appears in a solo acoustic set at the Fox Theatre on Thursday, March 7. After busting out of the stale Nashville of the late '80s with ballsy, rocking albums like Guitar Town and Copperhead Road, Earle served time for heroin possession. When he emerged from captivity, his face was more etched with experience, but he was also clean and sober. On 1995's Train A-Coming, he expelled the sour air of prison life like poison gas, offering a blend of blues, country and rock that was more finely honed than his earlier work. Transcendental Blues, Earle's most recent disc, is steeped in country blues but contains wildly varied styles such as Irish folk, some trippy psychedelia and even McCartney-esque pop; an album of B-sides is scheduled for release in April. Like the man himself, Thursday's show promises to be anything but predictable.