Cosimo returns from exile while his rival Rinaldo degli Albizzi faces trial for treason.
Cosimo was indeed exiled in 1433 by the Albizzi, but his return in 1434 effectively made him the "unofficial ruler" of Florence. Medici - Ascendancy ...
Many deaths in the show/book (like Giovanni or Lorenzo the Elder) are dramatized; in reality, most died of natural causes. Cosimo returns from exile while his rival Rinaldo