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KNOW IT ALL: Monday's Top 7 Stories at NBC News

The big sell-off on Wall Street and a honor for three Americans who stopped an attack in France are at the top of the news.

Good morning. Here are the top headlines from NBC News.

1. Wall Street Appears Headed for Another Dire Day

Buckle up: It looks like another bumpy day in the stock market. Dow Jones industrial average futures are down more than 400 points, and Asian markets are tumbling. Last week was the worst for stocks in four years. Read more in BUSINESS.

2. Heroic Americans Get France’s Highest Honor

The three Americans who helped thwart a gun massacre on a train last week met with the French president, who said their bravery helped prevent “true carnage.” Read more in NEWS.

3. ISIS Blows Up Roman-Era Temple in Syria

The temple is one of the most important sites in the ancient city of Palmyra. It’s the first time that ISIS militants have damaged monumental Roman-era ruins. Read more in NEWS.

4. North Korea Accused of ‘Unusual’ Military Activity

Marathon negotiations between North and South Korea have dragged into a third day. The South wants an apology, and the South Korean president says there’s “no room to back down.” Read more in NEWS.

5. Oklahoma Politician Stabbed to Death, Allegedly by Son

Mark Costello, the state labor commissioner, died at a hospital after he was stabbed in the head and neck outside an Oklahoma City restaurant. Police have taken his son into custody. A witness says there was a chase around the restaurant. Read more in NEWS.

6. Louisiana Police Officer Shot in Head

A state trooper suffered “severe neurological damage” when he was shot with a sawed-off shotgun, police say. The trooper is in critical condition, and the man accused of firing at him has been taken into custody. Read more in NEWS.

7. Jimmy Carter, Sunday School Teacher, Focuses on Love

Hundreds of people lined up in Plains, Georgia, for the former president’s 689th Sunday school class. It was the first time he taught the class since revealing doctors have found melanoma on his brain. Read more in NEWS.