When Henry James chose to, as he did in The Princess Casamassima, he could write about the political turbulence of his era with astonishing excitement and directness. The London underworld of terrorist conspiracies that entangles his hero comes alive under his pen with a violence that seems, more than a century later, only too familiar.             Young bookbinder Hyacinth Robinson, the illegitimate son of a nobleman and a woman who died in prison after murdering him, has been raised by an impoverished seamstress. Hyacinth has grown up sensitive both to the beauty of the world and to the human suffering caused by social injustice, and when he is drawn into a circle of radicals he promises to commit an act of terror—a vow he comes to regret when the lovely and bored Princess Casamassima takes him under her wing. As Hyacinth travels across Europe and encounters a richly varied cast of characters from all levels of society, he is increasingly racked by his agonizing dilemma—until he resolves it in a shocking action that carries the emotional force of classical tragedy.