Jezero City: Colony Four Mars (Colony Mars, Band 4)

When a colonist dies in tragic circumstances, just a few sols before a major terraforming experiment, Dr. Jann Malbec begins to suspect that all is not what it seems. Her fears begin to grow when every attempt she makes to investigate the death is thwarted by the ruling council on Mars.
In desperation she resorts to secretly recruiting a recently arrived colonist, Mia Sorelli, an ex-cop with a troubled past, to quietly look into the incident. But Mia has some very good reasons why she left her old life on Earth behind. Nevertheless, she reluctantly accepts the assignment even if it means hooking up with the malcontented, semi-sentient droid, Gizmo.
But what Mia uncovers goes way beyond anything she or Dr. Malbec could ever have imagined. As she investigates she begins to suspect that a terraforming experiment may be compromised by those who seek to undermine the future of the colony.
Mia must now face down her old fears if she is to save, not just herself, but the entire population of Jezero City.
About Jezero City:
This is the forth book in a sci-fi series set in a human colony on Mars. The science depicted is, for the most part, plausible. In other words, what's technically possible with either current technology or taking experimental research a step or two further. That said, you won't need a calculator or a slide-rule to enjoy the story.