The main point that I wanted you to spot is that 1… Kd4 allows mate in 3 with the beautiful 2. Qxd5+ Kxc3 (or 2… cxd5 3. Nb5#) 3. Qb3+ Kd4 4. Qc4#.
1… Kb6 also gets mated: 2. Nxd5+ Ka6 3. Nc7+ Kb6 4. Be3+ etc.
So Black has to consider capturing on b4.
1… Nxb4 is also no good: White has 2. Be3+ winning the queen at once and soon mating.
1… Qxb4 is a better try, but is met by 2. Nd5+, and if cxd5 White has several ways to mate: for instance, Be3+ and Qc7+.
That leaves 1… Kxb4, when, miraculously, Black can, it seems, survive. 2. Rb1+ Kxc3 3. Rb3+ Kd4 4. Bb2+ Kc5 5. Ba3+ Nb4 6. Bxb4+ Qxb4 7. Rxb4 Kxb4 is the computer’s main line when Black has a very large number of, mostly undeveloped, pieces for the queen. 8. Qc4+ Ka5 9. Qxh4 Be7 10. Qe1+ Ka6 11. Rf7 gets one of the back, but Stockfish still claims Black is winning. Perhaps not an easy position to play over the board, though.
What happened in the game? Black played 1… Kd4 but White missed 2. Qxd5+, instead playing 2. Ne2+ Qxe2 3. Bb2+. Now 3… Ke3 4. Bc1+ would have been a draw by repetition, but after 3… Nc3 White played 4. Qc4+ and soon mated his Barnet Knights opponent, helping the good guys from Richmond Juniors win the match.
There are very many books on the market, not to mention websites, which will enable you to practise finding winning tactics, sacrifices and checkmates. Learning to defend accurately is an equally important, but usually ignored, skill.
I forgot to mention that our sponsors were putting up a £1000 prize for the first correct solution, but as no one contacted me with the correct answer I get to keep the money myself!