This is the 2nd book in Riordan's Magnus Chase and the Gods of Asgard series. This series focuses on Norse Mythology. The first book in the series was The Sword of Summer, in which Magnus appears as a homeless teen who finds out he is the son of Frey, the Norse god of summer. He embarked on the heroic quest to find the sword of summer and ended up as a guest in Hotel Valhalla. He has made friends with Hearthstone (the deaf elf), Blitzen (dwarf), and Samirah al-Abbas (Muslim /Valkyrie / daughter of Loki). At the end of book 1, Magnus compares notes with his cousin Annabeth Chase from the Percy Jackson series.
In this book, the team from book 1 is sent on a quest to retrieve Thor's hammer, which he is always losing or someone is always stealing from him. Magnus learns more about his healing powers and Samirah meets her demigod sibling Alex Fierro, a gender-fluid child of Loki. They have to follow through on an arranged marriage to an earth giant in order to get close enough to the hammer to get it back. Shenanigans ensue as always.
Readers of Percy Jackson will find this series familiar. I felt some of the themes were a little more mature than in Percy, but the overarching theme is always a group of very different people finding a way to work together and respect each other to develop close friendships and achieve a common goal.