Marchant de Lange's 13th five-wicket haul in first-class cricket put Gloucestershire on course for a first County Championship win since the end of the 2022 season on day two of their Division Two clash with Northamptonshire.
The South African paceman, who'd taken a six against Middlesex earlier in the season, produced a consistently hostile bowling spell to return 5 for 42, including wickets off successive balls, as the hosts were bowled out for 171, 238 behind Gloucestershire's first-innings total of 409.
De Lange played his part in helping the visitors reach that total as his unbeaten 36, including two huge sixes, helped Josh Shaw add 71 for the ninth wicket, with Shaw matching his career-best with 44. Siddarth Kaul managed at least a five-fer on debut for Northamptonshire, finishing with figures of 5 for 76.
Gloucestershire, who haven't won at Wantage Road since 2010, declined to chase. Instead, openers Cameron Bancroft (36 not out) and Ben Charlesworth (41 not out) took the visitors to 77 for 0 and a total of 315.
Gloucestershire resumed on 338 for 8 and Shaw and de Lange quickly dashed any hopes Northamptonshire had of chasing down the tail with a ferocious attack on the bowling.
De Lange set the tone by slashing an early delivery from Ben Sanderson over fine leg for four and followed that up by hitting the same bowler over his head for six.
When Sanderson gave way to George Scrimshaw, de Lange deposited a short ball over mid-wicket for another six, which looked to be threatening the local ice cream van, but fortunately sailed beyond it onto the concourse.
Shaw caught the mood and drove Scrimshaw over the ropes for a fourth wicket before Kaul trapped him lbw to end the fun.
Northamptonshire's reply began in extraordinary fashion when Ricardo Vasconcelos hooked a short delivery from Ajeet Singh Dale over long-leg for six.
Fellow opener Emilio Gay's experience was at the opposite end of the spectrum as he was trapped lbw first ball by a swinging delivery from Shaw that trapped him plumb in front.
Vasconcelos, however, kept going, adding six fours to his earlier six as Northamptonshire went to lunch on 56 for 1 with little sign of the afternoon's carnage to follow.
De Lange, however, changed the mood within three balls of resuming play. Vasconcelos hadn't got his feet moving when he flicked one to James Bracey for 43, and Karun Nair was the first ball to be bowled at pace.
George Bartlett prevented a hat-trick and, for a while at least, he and Luke Procter threatened a revival.
Spinner Zafar Gohar cut the revival short, trapping sipper Procter on the crease for 32, and Bartlett was soon undone by an extra bounce from Tom Price, Bracey taking a fine catch at stumps.
Saif Zaib, restraining his usual aggression, resisted stoically for his 80-ball 23, only for De Lange to return and find the outside edge for Bracey to claim another victim and Zafar to return to have fellow spinner Liam Patterson-White lbw.
Invigorated by his afternoon tea, de Lange helped wrap things up early in the final session, Kaul and Sanderson both falling behind the wicket, the latter to a bruising delivery which flew off the shoulder of the bat to slip.