Leicestershire 174 for 5 (Ackermann 65*, Inglis 49) trail Middlesex 324 (Robson 154, Davis 5-66) by 150 runs
Leicestershire seamer Will Davis bowled his side back into contention on the second day of their LV= Insurance County Championship clash against Middlesex with season's-best figures of 5 for 66.
Davis, who had gone wicketless the previous day as Middlesex amassed 280 for 3 at Merchant Taylors' School, sliced through the lower and middle order to prompt a collapse to 324 all out.
Ackermann had reached 65 not out, with the visitors on 174 for 5, when bad light forced the players from the field.
It was Abidine Sakande who triggered the procession of Middlesex wickets, bringing one back to hit Joe Cracknell's front pad in the third over of the day before Davis took centre stage.
The Foxes paceman got the ball moving sufficiently to remove Robbie White and then Sam Robson, whose seven-hour innings of 154 came to an end as Josh Inglis took a diving catch behind the stumps.
Davis swiftly mopped up the Middlesex tail, dismissing James Harris and Nathan Sowter in successive overs and completing his five-for when Murtagh skied one into the hands of mid-off.
However, Murtagh struck back immediately at the start of the Leicestershire reply, with Sam Evans picking out Sowter at cover in the opening over before Lewis Hill was lbw to a delivery that kept low.
Marcus Harris - who shared a 243-run partnership with Ackermann when the Foxes chased down 378 to beat Middlesex at home earlier in the season - looked in good nick again, producing a string of boundary drives in his brisk 31.
The Australian left-hander departed when namesake James Harris persuaded him to edge behind, but Ackermann, who took 23 balls before getting off the mark, proved harder for Middlesex to shift.
He built a fruitful stand of 97 with the more pugnacious Inglis, who looked set to overtake his skipper to a half-century, but was left one short as he lost his off stump to Ethan Bamber on the stroke of tea.
That was Bamber's sole reward for two impressive spells, but Sowter held a sharp catch at midwicket to cut off Harry Swindells' powerful drive and secure a third wicket for Murtagh before the rapidly darkening sky brought play to a close.