Spoilers ahead.
I've been working my way through the free Kindle Henty's from Amazon. This is like my fourth one and probably the best so far. These books are really dated and anachronistic. Even taking into account that, I would still only give it a 3.
Story time: Harry is a 1/2 pay naval lieutenant and he wants to marry Ms. Fortescue. But her dad is a retired prominent lawyer and doesn't want his daughter to marry a penniless guy. The deal is that Harry will give it 2 years to make it big. If he does, he'll come back and get her hand.
Harry's guardian or trustee of his funds, Mr. Barnett knows of this lost Inca treasure and he arranges for Harry and his younger brother Bertie to go and look for it. They arrive in Peru where there's anarchy as various generals are fighting each other for power. The natives (called Indians at that time) and uninvolved.
They manage to find a muleteer named Diaz whose life was saved by Barnett on a previous trip. Harry also saves his life in an incident which binds Diaz to them. Understand that this is a boy's book from the height of British prestige and the Brits can't do no wrong and everyone is respectful of them. Anyway, Diaz, his wife Maria and his nephew Jose agree to go with Harry to look for treasure.
They first look for treasure inland. This is based on ancient oral legend passed down. Supposedly the treasure was hidden from the Spaniards but Diaz agrees to lead Harry to it since he saved his life and he has no need of money and doesn't care that Harry takes it as long as it's not the Spanish. They find the valley but unfortunately the valley has been flooded by the ancients to hide it and there's no way for them to get it.
But we get to see wonderous sites, both natural and real archeological sites as they travel inland. They also have to deal with "savages" which are native Indians who lived outside of contemporary Peruvian society, rogue soldiers and brigands. This portion of the book was in itself interesting since it gives a fairly good picture of what traveling in Peru was like at the time, basically a travelog that included fighting. But they don't find any treasure and regroup. By the way, I don't think Machu Picchu had been rediscovered by the West yet otherwise Henty might have sent them there.
The first attempt inland took up almost a year but still have a few months left. So they decide to look for treasure at a hidden haunted castle near the sea, another legend. I'm not sure if this castle is an actual historical site. Anyway, they do find this castle which is well hidden among the rocks. It's very well built by the Chimu civilization which predated the Incas (the Chimu are the original owners of the treasure, so it's not really Inca gold). They find a bunch of skeletons there and theorize that they had been left behind to protect the treasure.
They go about it with a will digging into basements and side walls but find nothing except for silver sconces which they take. It's taken them months and a lot of work. Finally they decide to check out a window that looks out to the sea and think that maybe gold was sunk outside in the bay. So they swim out and quickly find the treasure which had been sunk in a shallow protected area. They recover 200 ingots worth of gold and sneak it back aboard a English ship going home. Diaz continues to decline a share saying it's cursed but Harry manages to convince him to take the silver as well as some money from his own trust fund since that is not cursed.
I don't recall the numbers in the book but I calculated the gold to be $11M in today's money. Harry deposits the gold in the Bank of England and shows Dad Fortescue the receipt and he has no more objections since double his own retirement fund and Harry gets married and everyone lives happily ever after.
Alright, I do have to state again the disclaimer that this was written a long time ago, like 100 years. No way today would this be politically correct where you go into some other country, hike all over that country, shoot and kill natives and brigands, dig and destroy archeologic sites and steal their gold. No wonder the Brits were so bloodthirsty rampaging all over the world. But I don't really blame the writing. After all, modern movies are the same where adventures just go and dig up treasure without regard to the law or the historical sites.
The merit of the writing: The writing was ok. It was very slow in some places and could have been speeded up a lot. I call it slow writing. For example, when they talk about building a fire, Henty will describe gathering twigs, building up a cone, lighting the match, blowing on the fire to encourage it and finally adding wood. It's like 3 pages of words when he could have simply said: they built a fire from twigs and firewood lying around. There is a lot of this and I would usually fast read it.
OK, so apart from all the negative aspects, it was a pretty fun treasure hunt story on easy mode and had a happy ending. To use a modern analogy. It's like playing a video game where your task is to travel to a foreign country, kill people and dig up treasure, except it's a book, which is all kids had 100 years ago for fun. On to the next Henty!