George Dobell is a senior correspondent at ESPNcricinfo
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A few days ahead of this Test, Mark Wood spoke to the media in the team hotel in Antigua.
It was the latest in a series of conversations in which Wood insisted that, this time, he really had regained full fitness and he really could bowl fast again.
You wanted to believe him. You really did. But we had heard it all before and, when he said he could "maybe bowl as quick as" Shannon Gabriel, there were some rolled eyes. Those days, we thought, were long gone and several previous recalls had seen the talk unmatched by the reality. He invariably looked a good, whole-hearted amiable fast-medium seamer. And England aren't short of those.
But Wood was right. And here, in St Lucia, he showed what England have been missing all series. What they missed in Australia. What they dearly need to give their attack some bite: well-controlled pace bowling.
For make no mistake, this was quick. Thrillingly edge-of-the-seat quick. At one stage, Wood was timed at 94.6mph (that's 152kph) and, for the first six overs of his first spell, his average delivery was over 90mph. Gabriel's quickest delivery of the series has been 93.9mph. Yes, that means in this series dominated by West Indies' fast bowlers, a slim and not especially tall man from Northumberland has delivered the fastest ball. Less Fire in Babylon; more Fire in Ashington.
We do have to apply a little caution with such statistics. There has been little standardisation of the measurement of bowling speeds over the years and a tiny change in calibration might make a huge difference. At one stage on Sunday, Moeen Ali was timed at 90.1mph.
There was no mistaking the reaction of West Indies' batsmen, though. There was no mistaking the manner in which Roston Chase fenced one to gully or Shimron Hetmyer spliced one to first slip. There was no mistaking Shai Hope's dismissal, either. Rattled by previous deliveries - the ball before had been a well-directed bouncer which scudded past his helmet, the one before that reared past his outside edge - he pushed hard at a full one outside off stump and sent an edge to gully.
There were other good performances for England. Moeen Ali bowled as well as he has at any time on this tour - he has a good chance of finishing as England's highest wicket-taker for two tours in succession - and both Rory Burns and Stuart Broad held outstanding catches. From a West Indies' perspective, Kraigg Brathwaite's inexplicable slog to deep midwicket - a real shocker of a shot - was the catalyst to collapse.
But this was all about Wood and his well-directed pace. For pace can unsettle batsmen. It can rob them of their composure. It can make all the difference. Especially on surfaces like this which offer a bit of variable bounce. There is a real danger West Indies could be penalised for their pitch for the second Test in succession.
So, where has this pace come from? Well, for one thing, Wood has lengthened his run-up a little. He feels this puts less stress on his body and helps him retain his fitness. In 12 previous Tests, he had shown flashes of pace - there was a memorable spell against Yorkshire on T20 Finals Day in 2016, too - but he had never claimed more than three wickets in an innings.
"I thought I bowled faster on T20 Finals Day," he said. "That felt quicker. There was one - the Hetmyer wicket - that flew through to Rooty. That felt pretty fast. He's a huge talent so to get him out and make him look uncomfortable was really pleasing. And 95 mph... that was past expectations."
He might also be benefiting from some smart man-management. He was left out of the team at the start of the ODI series in Sri Lanka and was challenged by the coach, Trevor Bayliss, to put his potential into action. The sense was that Wood was just a little too amiable for the role of mean fast bowler. That he needed a bit of stick as well as a bit of carrot.
He responded exactly in the way Bayliss intended. He delivered some blistering spells in the nets and then went away on the Lions tour to show he could sustain such aggression. He claimed five wickets (four were in the first innings) in the only unofficial Test against Pakistan A in the UAE, and put himself in pole position to claim a place on this tour should injury rule out any of the first choice bowlers.
When Olly Stone - who really does look every bit as quick as Wood - had to return home with a stress fracture, Wood won another chance. There was every chance, aged 29, it might even be a last chance. Even he admitted he had started to have doubts. It was no surprise he rated it as the best day of his career; even better than claiming the winning wicket in the Ashes series of 2015.
"Trevor challenged me to go and show I was a step above the lads in the Lions and really set the bar high," Wood said. "In most the games I feel I did that and proved I was an international class bowler."
"It's nice to show some people who've probably doubted me in the past. I've even doubted myself that I can do it.
"Everyone wants to take the winning Ashes wicket, don't get me wrong, but if I could trade that feeling in for a few more five-fors I would. For me, this is better."
There is a concern, of course. Wood's fitness record is poor and, combined with his slim frame, there are doubts about how much bowling he can take. It might be relevant that, just before this tour, he married and went on honeymoon.
Maintaining the balance between rest and play is crucial for everyone, but for Wood the balance may be more towards rest.
For that reason, Joe Root has to look after him carefully. Here he bowled an eight-over opening spell - albeit one split by the tea interval (3.1 overs before; 4.5 after) - with his pace dropping to the mid-80s in the latter stages. Wood himself admitted at the end of the day that he had probably bowled two overs too many.
"The plan was to be three-four over bursts," he said. "But because I was taking wickets I probably bowled two overs too many. At the end I was getting a bit tired."
Root has little experience of managing fast bowlers - few England captains do - and has, in recent months over-bowled James Anderson and Ben Stokes to an alarming degree. He might do well to reflect on Michael Clarke's use of Mitchell Johnson during the 2013-14 Ashes when, whatever the match situation, Johnson operated in three- and four-over spells. It kept him fit, fast and fantastic. Root has to show the same discipline now.
As an aside, this was a spell that did nothing to enhance Jofra Archer's World Cup aspirations. His best chance of coming in to the reckoning is for one of England's experienced seamers to suffer a loss of form or injury. When Wood bowls like this, he is a great asset who also has the benefit of experience. Archer, who has only bowled in 13 List A matches, may have to wait.
Wood deserves this day. A more pragmatic fellow would have shelved their Test ambitions in a bid to stretch their limited-overs career. He's had three ankle operations, after all. But his boyhood dream was to play Test cricket and some dreams outlive pragmatism.
"I would never give up my hope of playing Test cricket," he said in Antigua. "Growing up it's the pinnacle."
This was a day in the sun he deserved. But the days in the sun England need are still to come in the World Cup and the Ashes. They have a gem in Wood, but he needs looking after carefully in the coming months. He could make all the difference.