Yeah, there might not be any warships in residence, but it would be weird for a port city (which Tashbaan clearly is, considering the Splendour Hyaline can dock there) to not have ANY defenses on the river. And Calormenes are not stupid and no stranger to plots and subterfuge. Tumnus's plan was the best option in a tight spot, but there were a lot of ways it could have gone wrong.

I don't think Cimorene is interested in writing a novel, but she certainly has the right raw experiences to transmute into an interesting story!

And yeah, sometimes you just need a break for a day, particularly when the 'day' in question isn't even daylit because the Doctor's navigation was screwy once again. :-)