And I looked, and behold a pale horse: and his name that sat on him was Death, and Hell followed with him. And power was given unto them over the fourth part of the earth, to kill with sword, and with hunger, and with death, and with the beasts of the earth.
- Revelation 6:8 (KJV)
Yarbro's now known for her genteel vampire romances and various "Quinn Fawcett" Mycroft Holmes adventures. TIME OF THE FOURTH HORSEMAN predates both, being a 1976 SF vision of the then-near future - *not* a historical fantasy in the time of the Black Death (see BLOOD ROSES), although as implied by the title, epidemic disease is a major concern.
FOURTH HORSEMAN addresses a popular SF theme of the 1960s-1970s: overpopulation. (The theme's popularity has declined somewhat, as the issues of real-life history have been far more varied: China's policies, for example, or various countries where voluntary birth control is *so* popular that an aging population seems destined to depend on a shrinking workforce.) FOURTH HORSEMAN's overpopulation is a universal problem, without issues of nationality, religion, or ethnicity.
A major motive in FOURTH HORSEMAN is that voluntary methods of population control have proven ineffective - setting the stage for a conspiracy using *in*voluntary methods. (The conspiracy aspect is no spoiler - the story quickly stipulates the conspiracy's existence and activities, concentrating on the resulting problems - the suspense involves who'll survive and under what conditions.) The specific tools chosen involve sabotage-from-within of the health care system, which routinely vaccinates against major diseases to the point that the diagnostic technology no longer recognizes typhoid, cholera, etc. (We're not told what diseases the machines *are* normally expected to identify - they're supposed to be doing *something*, after all - or why physicians would still be taught to recognize the symptoms while their techno-toys aren't.)
FOURTH HORSEMAN's characters are mainly health-care professionals - not just physicians, although that's the calling of the two protagonists: Natalie Lebbreau and Harry Smith. We begin with Natalie, whose professional and personal situation illustrates the problems caused by overpopulation even while she realizes that more and more patients show symptoms of diseases that they should never have caught, having been immunized against them: tuberculosis, polio, even smallpox. Harry, having seen the same things with his patients, joins forces with Natalie after a 3rd party, asked by both to run tests, accidentally brings them together.
Professionally, Natalie is considered a trouble-making idealist; she once tried to force Inner City Hospital's administration to help remove two abused children from their parents' custody. Her colleagues admitted the evidence of abuse, but claimed insufficient proof the *parents* were guilty. The kids died within six months, and her colleagues not only refuse responsibility, but use the incident as an example of previous inappropriate over-involvement. Natalie isn't shocked at her requests for tests being ignored.
But after one brush-off too many, she finds more than she bargained for when she talks her way into her administrator husband's laboratory in Inner City Hospital to run tests on her own. Not only is her diagnosis confirmed; she overhears Mark's seduction of another woman - obviously not his first infidelity...Mark catches Natalie on a return trip, and reveals that the Project - random batches of ineffective vaccine for many major illnesses - is an experiment in population control and has been going on for years. No explanation of why all the diseases suddenly reappeared *now*; Yarbro doesn't address a necessary corollary: reintroducing the diseases themselves, particularly smallpox.
Natalie and her like-minded colleagues - healers who aren't just in it for paychecks, including various nurses, paramedics, and ambulance drivers - concentrate not on exposing the scheme publicly - as the diseases reach epidemic levels, that'll happen anyway - but on trying to pick up the pieces, survive, and get the Project stopped (priorities vary according to character). The monumental folly of the villains, as Natalie and Harry point out, is that they unleashed several diseases at once - so even if a person received a real vaccine for cholera, say, they might be vulnerable to half a dozen other diseases. The stupidity is implicitly attributed to an ivory-tower disconnection from reality among the administrators participating in the scheme - but since one of them is an epidemiologist, the situation still isn't fully accounted for.
Now the "test area"'s health-care system is rapidly being filled to bursting with patients dying from all kinds of things - and the resources just aren't there to treat them all, as the city is quarantined. The healers themselves are at high risk, in more ways than one.
Yarbro's eye for detail, while not fully developed, is apparent in many places. Child abuse is mindblowingly common - logical consequence of diabolical overcrowding. (Natalie's family of three (one a domineering administrator) live in a converted 3-room cellar.) Even more common is child abandonment - the hospitals see those kids once they're suffering from malnutrition and exposure. These kids have opinions of their own, starting with bitter awareness that the establishment seems bent on killing them off, and understandable suspicion of authority figures.
The total effect is of a tense adventure story suffering from plot holes of varying degrees of subtlety - which in turn might be considered side effects of the headlong rush of events, as issues are raised but not addressed. This includes development of the main characters - Mark's arrogance, for instance, extends into his personal life, but inconsistently *doesn't* interfere where it would be inconvenient to the storyteller. The main bad guys are sometimes inexplicably sloppy, but Yarbro compensates in some surprising ways. Scene-setting is *very* spare, in stark contrast to Yarbro's historical novels.