The Bat was written in 1997 and it is a very young Harry Hole whom we see. When the story begins, he is barely in his 30s, already has had two major tragedies in his life, and is a sober alcoholic. The death of a young Norwegian woman in Sydney, Australia, puts Harry's first book far away from the cold and dark Norwegian environment that is so familiar to us fans. Rather than the dour and serious colleagues in Norway, we have colorful, dour, and serious Australian colleagues.
Harry's "babysitter" is Andrew, an indigenous person, actually one of the babies spirited away by the Australian authorities to be raised in "better" surroundings with a white family. Through him, Harry learns a bit of the indigenous folklore. The bat is a symbol of death in their culture, and death is what Harry finds. Considering how foreign Harry is, the Australian detectives are unnaturally accommodating, even letting him call the shots during tense times. Maybe they sense the greatness that will become apparent in later books in the series.
This is mandatory reading for Harry fans, because we learn so much about his background, family, and tragedies. It quickly puts into perspective what we've learned about Harry in the books onwards from Redbreast, the first book published in English but the third in the series. There's even some humor about how to pronounce his name, the Australians primarily resorting to calling him Harry Holy.
Some of the deaths in the book are bizarre and a little, but not overwhelmingly, graphic. Just warning you.
*The title actually translates to "The Batman," but the holders of the copyright to the American "Batman" would not release it for use in the translation.