This is book number 20 in the The Boxcar Children Mysteries series.
The Aldens are going with grandfather to visit his friend, old Cap Lambert, a retired riverboat pilot who lives in a cabin in the woods. To get there, the Boxcar Children take a wonderful trip down the Mississippi in a paddlewheel boat. But when they arrive at Cap Lambert’s cabin, they find some mysterious things are going on. Spooky phone calls, eerie flickering lights, strange dark figures. Is the cabin haunted?