Based on that cliffhanger, The Lincoln Lawyer Season 4 would adapt the sixth book in the series: The Law Of Innocence, which was published in 2020, seven years after Book 5. Per Connelly’s website, The Law Of Innocence ‘s description is as follows, so here’s what to expect:

It really seems like Lincoln Lawyer is setting up Michael Irby’s DEA cowboy as the real villain behind everything happening. At the outset of episode 5, as they sat in the Lincoln, DeMarco asked why Haller would want to help a cartel sicario leave prison anyway.