The Shackleton Sabotage (The Boxcar Children Great Adventure #4)

The Aldens chart a course for their next adventure - Australia and Antarctica!
As the children tour the famed Sydney Opera House, their next puzzle - and its key - falls right into their laps. They need to find the rightful owner of a rare Australian coin. Using their knowledge about Australia, the Aldens find the coin's owner, but a saboteur is again hot on their heels and nearly spoils their hard work.
Next up, the Aldens travel to frigid Antarctica, where they need to return an artifact ...