Story so far: Hampshire looked destined for a home quarter until their ruinous last-day defeat to Somerset, so they will have to make do with a trip to Derby. The hosts have been steady in the North Group, and finished with a flourish. They are a diverse side and their imported talent has impressed, particularly on the bowling side, with Matt Henry, Hardus Viljoen and Imran Tahir picking up 45 wickets between them.
In focus: Watch out if Liam Dawson bowls the first over of the innings for Hampshire; in the four games he has done so, that over reads: 5-0, 2-1, 1-1 and 1-1. Canny and parsimonious. Wayne Madsen has regularly done a similar job for Derbyshire. Madsen has had a remarkable season. His 522 runs are the third most in the competition and more than any Derbyshire batsman in one season, ever. He has also 13 wickets, has only failed to take a wicket twice, and has an economy of 7.17.
This game should also be a legspin fetishist's paradise. England have released Mason Crane, whose 11 matches have brought 15 wickets at an economy of just 6.6, and he and Dawson are normally joined in Hampshire's team by Shahid Afridi, who has 12 and is going at 7.2. For Derbyshire, Tahir has been a revelation. He has 17 wickets, including four for 17 in their last game against Worcestershire.
Key data: Hampshire have the joint-most Finals Day appearances, with six. Derbyshire are the only team among the quarter-finalists never to make it.
Prediction: Hampshire, but not by much
Glamorgan v Leicestershire (Wednesday, 6.30pm)
Story so far: Leicestershire flew out the blocks, starting by winning four from four (all on the road). They then went six games without a win, before four straight wins in a week saw them sneak through. Lovely bread, horrible filling in that sandwich. Glamorgan were the opposite: a consistent force in the South Group, with Welsh rain - four matches have been rained off at Cardiff - their only hindrance. They never lost two on the spin.
In focus: Glamorgan's excellence has been built on brutal batting in high-scoring games. They scored more than 175 in all but one (their chase of 99 in the rain-affected game against Middlesex on Friday) of their seven wins. Colin Ingram is their man: he hit two tons (both in victories where a batsman scored a century for the opposition) and 25 sixes in 11 innings. Meanwhile, none of their bowlers have gone at an economy under 7.8!
The key for Leicestershire has been consistency of selection. Seven men played all their group games, while two players featured in 12 and one, the skipper Clint McKay, 11 (that was enough time for him to chalk up 22 wickets). Luke Ronchi's fast starts and Mark Cosgrove's canniness at No. 3 are crucial with the bat (they both have 401 runs), while Mathew Pillans (100 runs down the order and 17 wickets) has been a revelation.
Key data: Glamorgan and Leicestershire have met just once in T20 cricket: at Finals Day in 2004 (the Welsh side's last appearance on the big day). Leicestershire won by 21 runs and went on to beat Surrey in the final. Just two players from that game - Darren Stevens and Brad Hodge - are still playing.
Prediction: Glamorgan's batting to prove too strong for Leicestershire's bowling in a high-scoring thriller.
Nottinghamshire v Somerset (Thursday, 6.30pm)
Story so far: The loss of Nottinghamshire's opening two games felt a distant memory as their batsmen, led by Alex Hales (who ended the groups with a strike-rate of 210), went large. They won eight of their next 11 (with two washouts thrown in) to secure a home quarter with time to spare. Somerset, meanwhile, have been altogether more turbulent. They pipped Sussex to this tie thanks to a mighty, massive victory at Hampshire in their final game, and ended with six wins (at no stage did they string more than two together), six losses and plenty of bad blood on social media.
In focus: Hales was Nottinghamshire's most eye-catching performer, but his opening partner Riki Wessels scored more runs and was the tournament's most consistent bat, and had a strike-rate touching 150, too. He scored 28 or more nine times (in 13 innings), including eight on the spin, as well as a 54-ball 110 against Derbyshire early on. Somerset should ignore him at their peril.
Somerset are the only team in the last eight without a batsman with 300 runs (indeed Gloucestershire were the only others in the whole competition in that boat), and their selection (and batting order) was very inconsistent - they used a total of 18 players. They will rely heavily on their spinners Roelof van der Merwe and Max Waller, their only two bowlers going at under eight an over.
Key data: Tying Notts down will not be easy at Trent Bridge: the lowest first-innings total there this season was 180, and all six non-DLS games there brought 360 runs, with four of them containing more than 400.
Prediction: Notts should be too strong at home.
Surrey v Birmingham Bears (Friday, 7pm)
Story so far: Quite how Surrey have a home quarter, no one knows - least of all them. They told the tale of the congested South Group, and were consistently inconsistent: won two, lost two, won two, had two abandoned, then lost three before winning three more. Confused? Us too. Much-changed Birmingham took a while to find their feet but also finished strongly.
In focus: This is the catty clash the neutrals wanted: the Dom Sibley Derby (not words we ever expected to publish). Expect bad blood and south London boos for Sibley after he chose to leave Surrey for Birmingham at the end of the year. Following an inexplicably unpleasant press release (which revealed elements of Sibley's deal) from Surrey, he left early, with Rikki Clarke returning home a few months ahead of schedule in exchange. Both are available: grab the popcorn.
With Ian Bell dropped, Birmingham have a very youthful look alongside their gnarled old Kiwi pros. Sibley, Ed Pollock, Sam Hain and Adam Hose are key batsmen, while Olly Stone is finally fit and Josh Poysden returned well in their final two games. Aaron Thomason is a punchy, talented all-rounder too but the key man remains Jeetan Patel: only McKay has more than his 19 wickets, and his economy of 6.67 is the best of anyone with 16 wickets or more.
Key data: Both Clarke and Sibley have seen a sharp upturn in form since their swaps: Clarke has eight wickets in five games (and economy of 6.47) for Surrey, while Sibley has two fifties in four knocks for Birmingham.
Prediction: Sibley to power Birmingham into a home Finals Day