Lost Souls by David Mack

The last book in the Destiny series ties up loose ends, surprises you, and points to a very different future for the Federation.

With the Borg determined to destroy all life in the Alpha and Beta Quadrants- not just the Federation, but all sentient life. The Federation and non-aligned powers band together to face the Borg threat. President Nan Bacco awaits in the Palais de la Concorde, helpless to do anymore to stop the destruction of the people she has pledged to protect. The captains of the Enterprise, Aventine and Titan have been given free reign to do whatever is necessary. While millions of lives are taken by the Borg, many light years away, the mysterious Caeliar have saved one small life.
I enjoyed the "cameos" by the daVinci- no one else would have thought of protecting a planet from the Borg by making it appear to disappear.
The ending is one I couldn't have predicted- and I'm not sure I like. It's too tidy. I am also not as fond of the Borg Origins story, much preferring the similar ones I have read in Strange New Worlds and Shinsei Shinsei.
I also did not like the free hand Mack took in killing characters- amkes me wonder if this is supposed to be cannon or not.

ST Destiny Book One: Gods of Night

Gods Of Night begins David Mack's trilogy detailing the crews of the Enterprise and they Aventine as they prepare to fight the Borg, and of the Titan as it discovers a planet encased within a sphere.
On the Aventine, Ezri Dax has risen to the rank of captain after the death of the captain and first officer while fighting the Borg. Unsure of herself, and feeling guilty about the conditions of her advancement, she must fight her own demons before she can command effectively. To make things harder for her, her attempt to unravel a mystery discovered by Jadzia ends in tragedy
On the Enterprise, Picard is plagued by the incursion of the Borg queen into his thoughts as he must prepare to engage the Borg, while battling insecurities about the momentous decision he and Beverly have made.
On the Titan, the crew has discovered subspace tunnels leading from Federation space to a strange planet completely encased in a sphere. When the away team shuttles down, they are kept the the strange inhabitants; a situation complicated by Deanna Troi's delicate physical and mental state.