Derbyshire 146 (Guest 49, Harmer 9-80) and 97 for 1 (Guest 56*) trail Essex 412 for 3 dec by 169 runs
A career-best Simon Harmer haul dragged Derbyshire into trouble at a rain-swept Chelmsford, as the visitors threatened to disappear down the gurgler in less than two days' play. Essex have made all the running in their bid to beat both their opponents and the elements here, and only an improved showing second time around - underpinned by a maiden first-class fifty for the impressive Brooke Guest - kept Derbyshire above water going into the final day.
With the rain sluicing down on Thursday afternoon, Tom Westley, Essex's captain, had looked out of the window and admitted winning would be a challenge. Scoring enough runs quickly while batting first, then taking 20 wickets in short order, that was the conundrum. "But I think the scripts that Essex generate for themselves over the last few years, you never know what's going to happen," he added.
Essex's scriptwriters have truly been red hot in recent seasons, and no player has had his name in lights more often than Harmer. Nine Derbyshire batsmen were dazzled by his star wattage, as the plot for this match took a familiar turn; only Dan Lawrence's dismissal of Billy Godleman on the second evening prevented a shot at all ten. "We try our best to create a bit of theatre around the bat," Harmer said afterwards.
After being railroaded by Lawrence and Westley with the bat, Derbyshire were then mown down by the county game's premier spinner coming the other way. So hapless was Derbyshire's capitulation, the sight of an ACME anvil landing on one of the openers on the way out from the dressing room after they were invited to follow on would not have caused much of a stir.
As it was, after Luis Reece dragged a drive on to his stumps in the third over - an act of self-destruction worthy of the Warner Bros studio - Guest and Godleman batted competently enough to see Derbyshire through to the close one down, maintaining their chances of escaping with a draw should the weather cut into proceedings once again on the final day.
"We haven't won too many games this season, so the biggest thing for us is to get this game over the line," Harmer said. "It's pointless taking nine wickets if it ends in a draw. Hopefully we can put it together tomorrow.
"As long as the weather plays its part - there's some rain around and we can't control that. As it showed tonight, when there was a bit of moisture on the surface it didn't grip as much, so we're going to have our work cut out for us. I think we're going to have periods of play when we just need to make sure we get the ball in the right area. Nine wickets, nine balls, it can happen pretty quickly at Chelmsford."
Derbyshire's best hope of surviving appeared to be by staying off the pitch, but after morning rain brought about an early lunch, play got underway at 1.10pm. Having been required to bowl spin under the floodlights on the second evening, Essex gave the seamers a perfunctory burst; Guest and the nightwatchman, Alex Hughes, knocked the ball around calmly enough and the thought occurred that Derbyshire might only need to bat well for a session to make the game relatively safe.
But that was before factoring in the local spin kingpin. Harmer was introduced after six overs, two wickets to his name already, and he wheeled away through the afternoon to round up seven more; this was the fifth time he had taken eight or more in an innings for Essex, and his eventual figures of 9 for 80 were the 13th-best for the county, and second-best at Chelmsford. Four of the six best innings analyses on the ground have been wrought by Harmer's dinner plate hands.
Hughes, the allrounder playing his first game of the season, showed as much nous as any of Derbyshire's batsmen in trying to neutralise Harmer. He employed the sweep to good effect, and lasted for the best part of an hour before being lured out of his crease for Adam Wheater to effect a juggling stumping. That brought Derbyshire's most-experienced batter to the crease, though Wayne Madsen was quickly in Harmer's sights.
He might have fallen third ball, sweeping in the air out towards deep square leg where Paul Walter couldn't cling on to a running, diving chance. A skittish innings came to a close the ball after he had lofted Harmer for a second six, done in the flight to turn a simple catch to leg slip; Madsen slumped on his bat handle, and Derbyshire were soon to be completely unmoored.
Despite the possibility of rain around - and play was again interrupted by a sharp shower shortly after Derbyshire began their second innings - none of the visiting batsmen bar Guest showed the intent to batten down the hatches for a lengthy stay at the crease. Matt Critchley, eighth on the run-scorers' list going into this round, slapped his sixth ball back to the bowler to complete a 23rd Harmer five-for in Essex colours, and Harvey Hosein went two overs later as Ryan ten Doeschate snapped up a sharp chance at short leg straight off the face of the bat.
Never mind the precipitatin', Harmer was prestidigitatin'. Guest was next to go, for what was at the time a career-best 49, as the ball looped up off the front pad to be taken by ten Doeschate - a hint of glove enough for Ian Blackwell to raise his finger, never mind Guest's crestfallen demeanour. Billy Stanlake never looked likely to last long, and although Dustin Melton hit Harmer out of the ground during a brief bout of tail-end tonking, a stinging return catch completed his haul. Derbyshire had lost six wickets in six consecutive Harmer overs, and the credits appeared ready to roll.

Alan Gardner is a deputy editor at ESPNcricinfo. @alanroderick