Shahrastani’s fame as a heresiographer and Sunni theologian rests respectively on the Milal and the Nihaya, and he was closely associated with the ascendancy of the Shafi’i and Ash’ari establishment of his period, even holding a position at the Nizamiyya in Baghdad. However from the later period of Shahrastani’s life come writings which demonstrate that he was influenced by, and even secretly adopted, Isma’ilism. In the incomplete text of his Qur’an commentary, The Keys to the Arcana (Mafatih al-Asrar), which survives in a unicum manuscript in Tehran, he outlines a complex and brilliant hermeneutical theory on whose basis he claims to gain access to the scripture’s higher meanings. In his belief, this system of hermeneutics derives from the authority of the Prophet’s family and lineage, and in fact many elements of his hermeneutics can be shown to derive from Isma’ili thought in his period, such as his concept of hierarchism (al-tarattub) and of opposition (al-tadadd). Underlying this hermeneutics is a controversial theory of the binary transmission of the Qur’an. On the one hand there is the ‘Uthmanic version which is accessible to all but which Shahrastani frankly views as problematic. On the other hand there is the codex of ‘Ali, the historical existence of which our author full accepts. Though this text is hidden from public view to protect it, it is implicit in the authoritative hermeneutics of the Prophet’s lineage. To have access to God’s Word, both channels must be combined. Shahrastani intriguingly suggests that the situation is comparable with that of Judaism, in which the Torah also survives in two transmissions: the prevalent (i.e., Masoretic) text, and also, supposedly, a secretly preserved copy of the Tablets as received on Sinai and passed on in the high priesthood (‘inda ‘l-khassati min awlad Harun).