Shabbat Zachor is the Shabbat immediately before Purim. We read a special Maftir that talks about the commandment to remember to wipe out Amalek, and then we read a special Haftarah which talks about how King Shaul was charged with fulfilling this commandment.
The text, Linear annotated translation of the Haftarah of Shabbat Zachor is not short, but it is full of drama and emotion.
While the connection between Parshat Zachor and the Haftarah is obvious – Amalek – how it connects to Purim is less so. See: The Reboot for how Mordechai, Esther, and Haman are all found in the Haftarah and why.