The Hour of the Gate (Spellsinger, #2)

Spellsinger Jon-Tom follows bespectacled turtle wizard Clothahump for allies against invading insect Plated Folk with new magic - and way home to our world. Crew is his crush Flor, 5' otter Mudge, red-hair Talea, big bat Pog, gambler Caz, dragon Falameezar. Froggy Bribbens guides them in split river under mountain but no farther to arachnid Weavers or mythical Ironcloud.