It is distinguished as the second appearance of the Ice Warriors.

The Ice Warrior's army is completely surrounded, and they realize all is lost.

One of the "green things", which the Doctor identifies as an Ice Warrior, appears.

However, the Ice Warriors want one particularly important artifact back.

He mentions the Ice Warriors and K-9 as if they were present.

The first stop in its search: Mars, home of the Ice Warriors.

Minutes later, they are ambushed and gunned down by the Ice Warriors, who leave them for dead.

Ice Warriors also have sonic weaponry built into their wrists.

This story, set in the 21st century, appears to depict the first full contact between humans and Ice Warriors.

Centuries later, some of these Ice Warriors were revived and eventually discovered a new home world.