The book assumes that you've done some stochastic analysis courses before. You need to be familiar with Girsanov's theorem (change of measure) and some PDE theories (Feynman-Kac) to better understand the materials. The book starts with the introduction of instruments in the interest rate market. Then before introducing the continuous-time models, it shows how to price interest rate derivatives/ZCB in a binomial model, the classical Ho/Lee model is also introduced. The chapter on short-rate models is good, it shows 2 different ways to price zero-coupon bonds, martingale approach and the PDE approach. The book even proves ZCB/options on ZCB under the Vasicek and CIR models (in the appendices). More recent developments such as LIBOR/HJM are also introduced.The book might be a littel bit difficult to read at the start (formal maths), however, it rewards perseverance.
P.S. the solutions to the exercises of chapters 1-5 can be found from A.Cairn's web-page.
P.S.2 note that the book does not give any details on implementing different interest rate models in practice.