When Evanlyn tells Will her real name on Skorghijl we hear Will's thoughts, he thinks that he is afraid of betraying Evanlyn to someone who has sworn to kill all of her family. It isn't until later that Will finds out that the oath Ragnak has given is to kill all of Evanlyn's family.

When Clay and Tom are threatening to break into the hotel, Tom says "I'm going to grab a kerbstone and smash the glass", but Clay says "A curbstone?" Since they both say it, there should be no spelling error.

When Graystripe and Firestar spy on the Tigerclan camp they name the cats in the clearing. Mudfur is among them but on the next page it mentions a lack of medicine cats. Mudfur is the medicine cat. As far as I know you can't unbecome a medicine cat.

In the second book it says that Artemis' father's last memory was waving goodbye to his family but in one of the diary extracts, when Artemis is at the hospital with his father, his father talks about his time as a prisoner, which he shouldn't be able to remember.

Dumbledore tells Harry at the end that Lord Voldemort is the last remaining ancestor of Salazar Slytherin. But ancestors are in the past - he means Voldemort is the last descendant of Salazar Slytherin. Not a mistake Dumbledore would have made. (Corrected in later printings.)