This paper investigates the cognitive mechanisms of idioms in Atwan's autobiography. The theoretical preliminaries of the research centre upon the three cognitive phenomena: conceptual metaphor, metonymy and conventional knowledge that prove the motivation rather than the arbitrariness of idioms. Macroidioms that indicate the macrostructural nature of idioms are singled out. The idiom frames which weave the fabric of the text are the prime interest of the researcher. The cognitive anatomy of the internal structure, the cognitive micromodel and the complex scene visualization of idioms are also brought into focus. The lexical network analysis of polysemous items in the idioms alongside with the polysemous human body idioms are also investigated. The hypothesis of the study is that the idiom develops an organic unity of a theme and builds it up throughout a given text with marked coherence by means of cognitive mechanisms and idiom frames.