First off, I absolutely adore this series. Rick Riordan somehow manages to successfully combine Ancient Grecian mythology, modern-day ideals and technology, along with plenty of wit and sarcasm to create these masterpieces. Recently, I have picked up The House of Hades (if you couldn't tell by the picture), this book being the fourth installment in Riordan's latest series, The Heroes of Olympus. The story is a direct continuation of The Mark of Athena, and occurs right after the events at the end of said book. 

Some spoilers may be contained below, so I would suggest you stop reading here if you'd rather to dive into this series with a clean slate:

The House of Hades follows two separate stories, following Percy and Annabeth as they traverse the perilous Tartarus, and Jason, Leo, Hazel, Nico and Frank while they travel across Europe in the Argo II. Both parties are attempting to get to the Doors of Death, so they can free it from it's shackles and get both Percy and Annabeth out of Tartarus alive. The group aboard the Argo II encounter various mythical beings and monsters, ranging from giant turtles and thieves, to the Goddess of snow, Khione. Percy and Annabeth, on the other hand, have to travel through the birthplace of monsters, where the taint of the acidic air weakens them with every step. Without supplies, and only the fiery water of the Phlegethon to keep them barely going. To avoid revealing any major events in the plot, I'll stop here.

But, all in all, I greatly enjoyed this book. Although I feel it's ending was a bit anti-climactic, and it didn't leave as much of a dramatic cliff-hangar as in The Mark of Athena, I loved learning about all of these intriguing Greek (and, I suppose, Roman) Myths, all while being caught in the troubles and tribulations of each and every character. I found it hard to put down the book once I was snagged.

Luckily for me, I picked this book up late, and the next book in the series has already been released. I must say, I can't wait to pick up the fifth book in the series, and plunge into the depth of the finale, The Blood of Olympus.