Hands are from Adventures in Bridge, October 17, 2018.
West (you) open 1♦ and North (LHO) overcalls 2♣. East and South pass. Since you are short in clubs, it is mandatory to reopen with a double. (With 4-4 in the majors, you would want to do so anyway.) Partner passes, converting your double to a penalty double. This is how you inflict a penalty (“positive”) double when playing negative doubles.
Partner gets off to an unfortunate lead with a low diamond. Declarer wins the ♦J in Dummy and plays a low spade to the ♠9 in her hand. Partner wins the ♠Q, then cashes the ♠A. She exits with another diamond. Declarer cashes both top diamonds and plays the ♥3 to partner's ♥2 and Dummy's ♥J. You win with the ♥Q.
It is time to take stock. Declarer had two spades (as did partner). Declarer had three diamonds (as did partner). Declarer started with three hearts (as did partner), so they both started with five clubs. Partner must have club cards behind Declarer and may need you to lead through. Put the ♣10 on the table. (Partner will know to play a heart back to you as you had nothing in diamonds and only the ♠K.) Your ♣10 smothers Dummy's the ♣8 and forces the ♣Q from Declarer. Partner takes the ♣K and returns a second heart to you. Now play the ♣9.
If Declarer DUCKS the ♣9, continue with a high SPADE to provide an uppercut for partner. That allows her to get back to you with one more heart. If Declarer takes the ♣A and plays her third heart, you play your high spade. Partner will get two more club tricks with her ♣J63 over Declarer's ♣754.
Declarer will go down at least three tricks, sometimes four—once again proving Budak's rule that if the defenders can make game (3NT in this case), Declarer will go down for MORE than the value of their game. Declarer goes for -500 or -800 and 3NT making four would be only +430 for E/W.
West passed, as did North. East opened 1♠ and South overcalled 2♦. Both West and North passed. East duly reopened with a double. West has a tough choice. You do have five diamonds, but no spots, though the ♦8 may well be worth more than it looks. On the other hand, you do expect to probably get a spade ruff. But you have NO other tricks. Defending will require your partner to have a really good hand for your side to score six tricks. But you don't want to risk 3♣ as partner might have only three clubs. You may elect to bid 2♠, putting partner in the 5-2 fit and hoping it works out. Or, you may gamble and pass, hoping to beat the contract.
If you pass, and lead the ♠7, partner will cash the ♠AK and then lead the ♠4 (lowest spade—suit preference for clubs). Declarer discards a heart as you ruff. You duly lead a club to partner's ♣A and she returns another spade. This time Declarer ruffs with the ♦10.
Your best bet is to discard a heart on that trick. Declarer must have started with three hearts. Your plan is to eventually lock Declarer on Dummy so you'll get an uppercut with your ♦8, Declarer will cash the ♣K and ruff a club on Dummy. Now he can run the ♦9, but you simply duck. He cannot get off of Dummy. When he tries to cash the second high heart, you ruff small and still have your ♦A for the setting trick.
If Declarer plays diamonds without ruffing a club on Dummy, you simply take the ♦A and return a diamond. You will get a club trick in the end instead of a diamond for the same down one. Unfortunately, nobody is vulnerable, so your plus 100 does not beat our the pairs in 2♠ and 3♣ who are making +110. C'est la vie.