Magid is absent from his family's drama—and much of the plot of the novel—for eight years, because his father sent him to Bangladesh. When he comes back, he ends up smack dab in the middle of everything. The narrator says, "The return of Magid Mahfooz Murshed Mubtasim shook the houses of Iqbal, Jones, and Chalfen considerably" (16.33).
Samad's plan in sending Magid away was to turn the boy into a real Bangladeshi Muslim. But, as Samad says more than once, Magid comes back "more English than the English." He speaks perfect British English (according to Mickey of O'Connell's), and wants to be a lawyer. Magid left in pursuit of one identity, and returned with another.
Where Magid's brother, Millat, adopts an extreme set of religious beliefs, Magid abandons religion and traditionalism to invest himself in science.
Magid is a bit of a tricky character to unpack because we don't get much clear insight into his motivations. We imagine, though, that being basically kidnapped by his father and his BFF to be sent to Bangaldesh for eight years kinda had a strong effect on him. As his father pushed him to become the perfect Muslim, he became the exact opposite: a wanna-be Englishman with a rational bent.