This was the first one of Ms Pietsch's Task Force 125 books that I read (free from Amazon UK). It clearly is a sequel but was easy enough to read as a stand-alone.
Task Force 125 is a Dark Ops team, based out of Las Vegas, operating in Europe. Sarah is the honey-pot that they use to obtain intel on/from various international lowlifes before the team eliminates them - permanently. Along with Sarah is a group of drop-dead gorgeous former military types (one is FBI, one a Recon Marine, one a SEAl etc).
What is refreshing about this series is that Sarah is a REALLY strong female character. In the first book she gunned down pirates (dressed in a bikini) whilst the rest of her team were pinned down without weapons, she also murdered two arms dealers in close physical quarters - one of whom she found very attractive and had been sleeping with for several weeks. She is a hard-drinking, smoking, swearing woman who speaks her mind and stands up for herself.
In this book Sarah is tasked with getting close to "Mr Big" in the arms dealing business and placing bugs to allow the team to identify his entire network before they wipe him out.