'Tunnel to Tar-Ra' is the exciting the story of perilous adventures of four fictional teenagers who travel back in time. Investigating a tunnel leading from Sydney's 'Hero of Waterloo' hotel, they eventually find themselves in a cave, in 1791, near Sydney Cove. During their first afternoon, overlooking Dawes Point (Tar-Ra), Jemima, Oliver, Millie and Archie, meet Nanberry, an Indigenous youth. Nanberry commences covert assistance by helping them with a secluded night bush-camp.

The time travellers have stepped into a living history book. As recorded in journals, letters and reports by the British First Fleet settlers of Sydney Cove they meet Aboriginal and convict people, they witness or hear of events and see the settlement living conditions of those times.

During their adventures the time travellers experience some living conditions in Sydney Cove. They witness an amputation, the flogging of a convict and the daring ocean escape of convicts William and Mary Bryant. They meet and engage with diverse inhabitants who lived in Sydney Cove at the time and learn so much about those early settlement days. Seeing the plight of the Indigenous people firsthand does not escape them.

After witnessing clandestine events, the youngsters become separated. With Nanberry and Boorong's assistance they reunite on Me-Mel Island (Goat Island). Whilst on the island they share campfire stories that provide an opportunity for readers to consider ethical issues.

They eventually locate the entrance to the cave that can lead them back to modern-day Sydney.