Solemn Duty is the 11th book in the Survivalist series. 

Fleeing an army of the infected, Deputy Marshal Mason Raines is forced to enter an area overrun with lawlessness. When his ex-lover is kidnapped, he must negotiate her release with a brutal warlord set on expanding his empire. Coerced to do his bidding, Mason is recruited to hijack a secret convoy running between the newly-established colonies. After discovering it contents, however, he must decide between the life of someone he loves and those of the pandemic’s last survivors. 

Meanwhile, Tanner and Samantha continue their pursuit of the gold stolen from Fort Knox. When they discover the train used to carry it away, they also encounter a small community plagued by grotesque body-snatching mutants. To recover the gold, they must undertake a dangerous quest to rid the area of the hideous monsters. But as the journey takes them into an abandoned missile silo, they make a discovery far worse than any they could ever have imagined. 

After taking her revenge, Issa awaits Tanner’s return to Mount Weather. When a young widow is brutally murdered, she must uncover not only her killers but also their reasons behind it. Discovering that the killing was a precursor to something much larger, Issa must choose between the safety of her unborn child and that of the community’s beloved matron.