Episode 1 - The Unsavoury Migrant
European settlers in the middle of the 19th century introduced the common carp the most widely cultivated food fish in the world, to Australian rivers. A research program has discovered that the carp is here to stay, but in limited numbers their presence is not as damaging as was once thought.

Episode 2 - Toad in the Cane
The marine toad is the largest toad in the world. In Australia it is called the Cane Toad and today is the most common amphibian in Queensland and many areas of Northern Australia. At present little can be done to stop the spread of the cane toad.

Episode 3 - Those Darn Cats
The cat came from the First Fleet in 1788. It came as a pet, and stayed as a hunter. From the cities to sub-Antarctic Islands and the arid deserts of the inland, the cat has spread throughout the continent. Today, the feral cat is regarded as one of the most deadly and dangerous of all intruders that were brought to Australia with European settlers.

Episode 4 - The Quick Red Fox
Englishmen eager to continue the sport they had enjoyed in Europe introduced the fox to Australia. The fox is a killer responsible for the decline in numbers of many native animals, from birds and mammals to the long-necked tortoise of the river Murray.

Episode 5 - This Little Pig
Millions of pigs in Australia never reach market. They are wild pigs that outnumber farm pigs four to one. They cause millions of dollars of damage each year to farms; breaking down fences, trampling crops and killing and eating lambs. The wild pig is potentially the most dangerous of all intruders.

Episode 6 - Deer Oh Deer
Six species of deer live in Australia scattered in small populations throughout the continent. Introduced as a game animal it is still-hunted although this is strictly controlled. Little is know about the effect deer have on native flora and fauna, posing the question: when is an intruder no longer a dangerous intruder.