A motor boat chugged a few times, the plash of an oar followed, then more shouts.
"I simply must find out what is going on there," muttered Harriet.

"I wonder if it can be--Yes, I'll row a little further along.

No one will see me unless I get within range of the lanterns there." Taking careful note of the entrance to their secret creek that she might recognize the spot when she returned, Harriet crept to the stern of the rowboat and using one oar as a paddle propelled the boat through the water as quietly as possible.
As she neared the scene of activity the voices of the newcomers grew louder.

Harriet finally ceased paddling and permitted her boat to drift, steering well into the shadows, hugging the shore of the island until she could touch it with an oar.

Unless she splashed with the oar, she was reasonably certain of being able to avoid discovery.