Deceit, Adversity, Affliction — John B. Bolton

In this novel, Capt Buckton upsets his wife Kate when he doesn't choose to go to her home world Pollux to assist a Medical Investigative Team (MIT) that is investigating a virulent epidemic that is extremely deadly and so far unstoppable.
Instead of going there he chose to go back to Transcia and Lutens, not to make war against them, but to assist them. The Translutens have been invaded by the Hamates, a powerful mind-reading species who live only to make war and conquer the next planet.
Things get really interesting when FltAdm Jensen informs JT that he will have some help in the form of several Mongon warships. The race of "metal beings" Capt Buckton and crew first met in their last venture into the EQ, the Mongon are the alliance's newest prospective member and are willing to show how good a member they will be by assisting JT and the Translutens.
As it turns out there is one double cross after another and nothing is as it appears and just trying to figure out what to do gets tougher by the minute.