To read two earlier columns on this subject click here (part one) and here (part two).
The 'Mother of all "double-or-pass" problems', below, is not named as such because it is a difficult problem (it isn't) but because the consequences of the wrong decision were so spectacular.
The deal is from the Germany − Sweden match during the 1997 European Teams Championships in Montecatini (Italy). Swedish crack Peter Fredin was faced with the following problem (?) — by the way: according to the championship's Daily Bulletin the player in question was Fredin's partner Eriksson but all later publications make it clear Fredin was the culprit:

N/—
♠	A K 10 6 3 2
♥	6 2
♦	Q J 6 4 3
♣	—

Should West double or pass?

West's 2♠ bid is one of the very few bids in an opponent's suit that is natural. It says: 'So what if South has a weakish four-card spade suit? That doesn't bother me since I have at least a good six-card spade suit and a very good hand.'

But what in heaven's name does North's 4♠ bid mean then? It cannot be natural, since West and South have at least ten spades between them. Furthermore: of course North knows West to have six or more. So despite South having bid spades first: after West's 2♠ bid spades is no longer 'NS's suit' but 'EW's suit'! So North shows shortness in spades; probably he has a void, a 0-5-4-4 distribution and a good hand.
But how then could South pass North's 4♠ cue-bid? The only possible explanation: South has fallen asleep and thinks North is showing spade support.
All is clear then: West should pass. NS will go down a lot, while they probably can make at least game in clubs or hearts.

In reality it turns out NS can make 7♣:

N/—		♠	—
		♥	A K Q 10 3
		♦	A 10 9 7
		♣	K Q 7 6
♠	A K 10 6 3 2			♠	Q 9 8
♥	6 2			♥	J 7 5
♦	Q J 6 4 3			♦	K 8 5 2
♣	—			♣	J 10 8
		♠	J 7 5 4
		♥	9 8 4
		♦	—
		♣	A 9 5 4 3 2

Since that day a double like this is known as a 'Fredin double'.

At the other table things went badly for Sweden too:

North's pass over 4♠ (he left the decision to his partner, who probably even might have passed) probably is too passive (compare with the intrepid bidding of his colleague-North at the other table!). In view of West's telling message that South has little or no strength in spades, North can visualise a slam. Whether a grand slam is biddable is hard to say (preferably 7♣ of course, since 7♥ is defeated by way of a club lead).

Double dummy NS could have defeated 4♠ by three tricks (diamond lead; South can eventually make three diamond ruffs): +500 to NS. Of course (how was he to know?) North didn't lead a diamond. But when he didn't succeed in giving his partner a single diamond ruff and somehow failed to make two diamond tricks himself, he even allowed West to make his contract. Another +590, meaning 19 IMP to Germany.

2007, ten years later: the Cavendish, the annual Butler (meaning: IMP-scoring) 'big money tournament'. Preceding the play the participating pairs are auctioned. The 'owner' of the eventual winning pair pockets hundreds of thousands of dollars. The winners themselves cash in a bit less, but still a small fortune.
Again Fredin plays a major part:

E/All
♠	K 7 6 4 3 2
♥	K 10 8 6
♦	9 6 2
♣	—

¹ Muiderberg: 5-4⁺ spades-minor suit, 6-9 HCP

After having beaten the big drum by leaping to 5♠, Fredin faced our familiar problem: to double or not?
Whether a double now is Lightner or not, is debatable (North has more or less been pushed into a slam) but that question is not important, this time. After all, West can judge that a club lead by his partner is not needed to defeat this slam: North will go down anyway. Possibly the slam will even fail by two or three tricks, since West's leap to 5♠ forced North to gamble (therefore a double probably isn't so much a Lightner double but simply 'gotcha'). A double may be very profitable, therefore.
On the other hand: hearts is the only suit against which Fredin has defensive strength. Can NS escape? To...7♣ for instance? That would be ironical, if we recall the last deal.
As it turned out the 1997 deal hadn't caused Fredin a severe trauma, for he doubled.
How will he have felt, after this continuation:

And yes: +2330 to NS:

E/All		♠	10 8
		♥	A Q J 7 5 2
		♦	A K Q
		♣	5 4
♠	K 7 6 4 3 2			♠	A Q J 9 5
♥	K 10 8 6			♥	3
♦	9 6 2			♦	J 10 8 3
♣	—			♣	9 6 3
		♠	—
		♥	9 4
		♦	7 5 4
		♣	A K Q J 10 8 7 2

I wonder whether more Fredin doubles are to be expected...