A possible concise summary is:
This is a story about how Abigail, a wise and beautiful woman, saved her foolish and wealthy husband Nabal from David's wrath. David, who had protected Nabal's sheep from raiders, asked for some food as a reward, but Nabal refused and insulted him. David was angry and planned to kill Nabal and his men, but Abigail intervened with a generous gift and a humble appeal. She persuaded David to leave the matter to God and not to stain his reputation with bloodshed. David accepted her gift and praised her wisdom. Soon after, Nabal died of a heart attack and David married Abigail.
Here are the key facts extracted from the text:
1. Samuel died, and all Israel assembled to mourn for him. (1 Samuel 25:1)
2. David left and went down to the wilderness of Paran. (1 Samuel 25:1)
3. Nabal was a rich man in Maon with 3,000 sheep and 1,000 goats. (1 Samuel 25:2-3)
4. Nabal's wife's name was Abigail, and she was intelligent and beautiful. (1 Samuel 25:3)
5. David sent 10 young men to greet Nabal and ask for food and drink for his men. (1 Samuel 25:4-9)
6. Nabal responded by asking who David was and refused to give him anything. (1 Samuel 25:10-12)
7. David was angry and prepared to attack Nabal, but Abigail intervened and brought gifts to David. (1 Samuel 25:18-31)
8. Abigail bowed down before David and asked him to forgive her husband's transgression. (1 Samuel 25:23-31)
9. David accepted Abigail's gift and forgave Nabal, but said that if she hadn't intervened, he would have killed Nabal. (1 Samuel 25:32-35)
10. Abigail returned to Nabal, who was drunk and celebrating, and didn't tell him about her encounter with David until the next morning. (1 Samuel 25:36-38)
11. Nabal became ill and died 10 days later. (1 Samuel 25:38)
12. David heard about Nabal's death and praised God for avenging him. (1 Samuel 25:39)
13. David sent word to Abigail proposing marriage, and she accepted. (1 Samuel 25:39-44)
14. Abigail became David's wife, along with Ahinoam and Jezreel. (1 Samuel 25:42-44)
15. Saul had given Michal, his younger daughter, to another man, so David was not married to her at the time. (1 Samuel 25:44)
16. David would later get Michal back in 2 Samuel 3:13-16.