All I can say after finishing this book is... 
 I HAVE TO WAIT ONE YEAR?!!!! 
 The spoiler section below will be a summary of the book for myself for next year when the 3rd book comes out. Jenny, this is generalized so some details may be missing... 
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 - First of all, Thor and losing his hammer. Hence the title! 
 - They went on a crazy adventure that consisted of 6 days! 
 - We meet Alex - a gender fluid child of Loki that became the recent einherji 
 - Barry is Sam's flight instructor! Amir helped get her lessons! 
 - Alex can withstand Loki's hold on her/him. Alex wants to teach Sam but is frustrated because Sam refuses to shapeshift. Alex believes Sam could resist if Sam would embrace that side. So Alex is waiting for the day Sam will open her eyes to change. 
 So we started off with Sam & Magnus meeting up. However, Sam had something to do which then leads to Magnus seeing a the tip off goat himself. However, as Otis was explaining, he was later killed by Utgard Loki - and we later find out why! 
 We see why Alex was brought in by Sam and they are super happy for her kill. However, Alex seems to be wreaking havoc in Hotel Valhalla prior to her being revered as someone who definitely deserves being an einherji. 
 So major plot here revolved around Loki's plans of freedom. He enlisted Thrym and Thrynga to wed Samirah so the bride gift - the Hammer of Thor would be given back to the crew while they get the sword of Skofnung. So when they had the tip off, they headed off to this area that seemed like a trap - which ends up unsurprisingly being a trap, fights off a bunch of zombies. In this scene we see that Sam can be controlled by Loki despite him not physically being there. Since she was knocked unconscious, Skofnung could be unsheathed and Uncle Randolph stabbed Blitz (Hearth actually predicted this and became mad at Sam for letting this happen to Blitz). 
 Magnus, despite his healing powers couldn't heal Blitz. They required the sharpening stone but that is with Hearth's father. Having no time and no other options, Magnus decided to turn Blitz into stone so they could have a bit more time to heal Blitz. Sam departed to do whatever she does while we journey with Hearth, Blitz and Magnus to Hearth's hometown of Alfheim. There, we see that Hearth's father is rich but cruel due to his brother's death and that the Son of Frey is actually super popular here. 
 To negotiate for the stone, Hearth had to fill up the entire blue rug (it was actually made from the monster that killed his brother) with gold before he would be released from this cruelty. However, under their time constraints, the servant of the house, Inge, had told them to seek out the Careful One, aka. Andvari. (Also, there's a question posed for later on in the books stated by Andvari - that since Hearth came back now, he will have to stop by again for something. Presumably the inheritance rune left by the well for his brother. He's been missing this rune.) They took all his gold, and his ring for insurance to ensure that the rug would truly be filled. We later see that the ring does corrupt the user and despite the short time Magnus had it on, he was also tempted by the gold it promised. However the ring was later given to Hearth's dad who became a bit crazy due to the ring's curse. They did save Blitz though which is great! (Inge was subsequently released by Hearth and she also confessed his love to him. I wonder will we ever see her again?) 
 When they were running from Alfheim, the portal to the nine worlds opened around the well (where Hearth's brother had died) and despite Hearth refusing to use that spot, they had to and was transported back to Midgard. Here, they parted ways and Magnus met up with our usual crew, Halfborn, Sam, Alex and Amir. Sam & Amir were arguing - because Sam was trying to get Amir to see. With the help of Magnus, Amir did see and together, they went to Bifrost and met with Heimdall (who loves taking selfies). Through Heimdall, they found where to go to seek out Utgard Loki and seek out whatever help he had to give. 
 Fast Forward: 
 Sam & Hearth separated from the team because she had a stallion fly the rest of them through the portal to Utgard Loki. However, they had to waste a day there since Tiny the giant had left Magnus, Blitz and Alex with a quest of bringing his bowling bag to Utgard Lanes. Blitz had crafted the bag into what he had been wanting to prototype and with Jack's help, the bag with a password can become big or small (and weigh close to nothing!) by saying the special word. Once there, they had gotten Tiny's word of giving them guest privileges. There, Utgard Loki told them of Loki's plans and how they had each played a part in securing Loki's escape - but I think that came with outwitting the giants at their games. 
 Sam had an ax challenge in which she discovered Fear hiding among them and won. 
 Hearth - god of the pinball machine. 
 Blitz - the ultimate makeover. 
 Magnus & Alex - a crazy game of bowling. 
 After all that, the giants still wanted to exact revenge on their humiliation and thus, they were chased of Utgard Lanes. They had help in escaping by Thor's wife in which they ended up speaking to Thor and told them their plans of getting back the hammer. Alex will pretend to be Sam and marry Thrym in her place. 
 But like most plans, this also went to poop since the giants were going to go to Loki's cavern to enact their wedding. This threw off the gods' and crews' plans and they had to quickly change the location. However, everything was a bit late as Skofnung was unsheathed despite there being female in the room and Uncle Randolph had freed Loki. Despite ruining the wedding and retrieving the hammer of Thor, they had let the captive and his wife free. 
 Upon returning, they were celebrated as heroes but the heroes felt like shit. (As per usual) But Helgi reassured them that they would be the team to chain Loki back and redeem themselves (and not allow Ragnorak to happen). They had to stop Loki from finishing his ship of nails which will sail in Midsummer. This means that Sam has to locate this area and Magnus has to sail with them. However, from the first book, Ran had stated that they would have trouble navigating the seas if Magnus tries. In which he enlists the help of his cousin Annabeth. 
 In the last chapter, and I guess if we really read into it, we can see ties to the Apollo book to this one!!! Because connections via wifi, text were all being wonky, but I digress. Anyway, in the end, Riordan hints that in the next books to come, Percy and Annabeth may be enlisted to help Magnus get Loki back!!!!! 
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 This is all so exciting. How do I even wait????!!!!!