Charles D. Bailyn

The observable features of black holes, both stellar-mass and supermassive, described semi-technically (some knowledge of college-level physics and math being required in some places). The features include accretion disks, jets, spin, and gravitational waves. In the brief discussions about black holes' more purely theoretical aspects, there's no mention of the recent fooferaw about whether "firewalls" lurk inside event horizons.