For a late night read when I was recovering from a cold this was exactly the book I wanted. I knew who the characters were, I more or less knew the rules of the universe, and I knew that there would be a few surprises coming.
The familiarity with the characters is essential for Portal; this is an ensemble novel that only works if the reader already believes that this team is a family forged in fire. It makes the critical parts of the novel sing, and that’s as much of a spoiler as you’re going to get here.
I did feel that one of the later elements  was perhaps a bit rushed, but I’m prepared to forgive that as the price of a very tightly edited book. Portal is only about 300 pages making it a short(ish) novel for the ground it covers.
If you enjoyed Boundary and Threshold, you will find Portal to be a satisfying conclusion to the stories of Helen, A.J, Joe, Maddy, and Jackie .