Bear in mind that readers may come to a sequel months, or even years, after reading the first book, or possibly not in order. Always recap the plot and describe the characters again to refresh their memory as well as assure any new readers don’t feel lost.
I run into this a lot, and have even caught myself guilty of this while writing my series. To the author, it is one continuous story. To the reader, however, who may have read the predecessor ages or at least many books ago, remembering exactly what was going on as well as the function of minor characters, is often unclear.
In some cases, you may want to use a prologue or a “The Story so Far” section for this purpose. Those who don’t need the review can skip it while those who do will appreciate it and allow them to get fully engaged in the story more easily.