"An Uncertain Sea" is the third and final book in the Don DeFreese/USS Mulligan series. The story opens with Commander DeFreese facing a Court of Inquiry over his conduct during the ship's most recent deployment ("The Persian Paradox").

In the meantime, to address challenges being posed by the People's Republic of China, the US Navy undertakes to shift resources from the Atlantic to the Pacific Fleet. The USS Mulligan, in a yard repair and maintenance period, is rushed out for Refresher Training at Guantanamo Naval Base, and from there, to the U.S. Seventh Fleet for operations in the South China Sea.

After the 2020 election cycle, a Democrat Administration takes power in January of 2021. Turmoil in the Middle East drives the Administration, in an ill-considered decision, to then divert Seventh Fleet assets to the Middle East. While the Administration's attention is not focused on the Western Pacific, China, having misread the new President's view of the PRC, decides to 'restore' the renegade province of Taiwan to Beijing's control.

Unable to develop a coherent strategy as tensions escalate, the Administration dithers while the Naval arm of the People's Liberation Army launches an invasion of Taiwan. The White House eventually decides a Seventh Fleet show of force will be sufficient to calm the situation. Instead, it provokes a further escalation of hostilities, and puts Carrier Strike Group Five, and the USS Mulligan, in harm's way.

Meanwhile, the ambitious Democrat Vice-President, dissatisfied with the inability of the elderly President to come to any decision, and with an eye to the 2024 elections, attempts to order expanded air strikes against Chinese forces. Any resolution of this great power competition will come at a great cost to the US Navy.