Elizabeth "Eli" Olmedo No, this novel easily stands alone. I had read #2 but not #1 and had no trouble following. Even if I hadn't read #2, it wouldn't have been an issue.
Paul Phillips No. Tessa Leoni is only a secondary character, and not very important to the plot (it really could have been anyone). Gardner's inclusion of characters from other books is largely unnecessary.
Samantha Kilford Nope. I had not read this first two prior to this novel and had no trouble understanding what was going on. I will have to go back and read #1 and #2 as #3 was exceptional.
Evelyn I have not read either 1 or 2, and am in now way lost reading this one. Enjoying the heck out of it!