A few of the books in Rebecca Zanetti's Deep Ops series are on sale
Hidden (#1) for $1.99
Taken (#1.5) 99¢
Fallen (#2) 99¢
Links go to the individual book page on her author site which in turn has the links to most of the various storefronts (Kobo, Google Play, Amazon, iTunes, etc)
Hidden (full-length)
Taken (novella)
Fallen (full-length)
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Book 4 will be out in January and I've been waiting for this couple since the start.